It could be reasonable to collect some past examples of such proxies. This would help in assessing whether something like this is technically feasible. Also I assume that if something like this is implemented at some point, we'll need to prepare list of regular expressions for such automatic rewrites - so it is good which proxies we are concerned with. (The post is CW, feel free to add more examples.)

 * `proxy.library.adelaide.edu.au`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.library.adelaide.edu.au) 
 * `proxy2.lib.umanitoba.ca`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy2.lib.umanitoba.ca)
 * `ezproxy.cul.columbia.edu`; only [1 ocurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.cul.columbia.edu)
 * `proxy.library.cornell.edu`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.library.cornell.edu)
 * `ccny-proxy1.libr.ccny.cuny.edu`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=libr.ccny.cuny.edu)
 * `ezproxy.fau.edu`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.fau.edu)
 * `ezp-prod1.hul.harvard.edu`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezp-prod1.hul.harvard.edu)
 * `libproxy.mit.edu`; in total [4 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=libproxy.mit.edu)
 * `proxy.library.nd.edu`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.library.nd.edu)
 * `ezproxy.library.nyu.edu`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=library.nyu.edu)
 * `ezproxy.lib.ou.edu`; [2 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.lib.ou.edu)
 * `ezproxy.lib.purdue.edu`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.lib.purdue.edu)
 * `libproxy.smith.edu`; in total [2 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=libproxy.smith.edu)
 * `libezproxy2.syr.edu`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=libezproxy2.syr.edu) 
 * `lib-ezproxy.tamu.edu`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=lib-ezproxy.tamu.edu)
 * `ezproxy.tcu.edu`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.tcu.edu) 
 * `proxy.uchicago.edu`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.uchicago.edu)
 * `proxy-remote.galib.uga.edu`; in total [5 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy-remote.galib.uga.edu) 
 * `proxy.lib.umich.edu`; in total [5 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.lib.umich.edu)
 * `ezproxy.lib.utexas.edu`; so far [3 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.lib.utexas.edu)
 * `libproxy.wustl.edu`; in total [3 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=libproxy.wustl.edu)
 * `ezproxy.weizmann.ac.il`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.weizmann.ac.il) 
 * `ezlibproxy1.ntu.edu.sg`; in total [3 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezlibproxy1.ntu.edu.sg)
 * `proxy.ub.umu.se`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.ub.umu.se) 
 * `ezproxy.is.ed.ac.uk`; only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.is.ed.ac.uk)
 * `ezproxy.webfeat.lib.ed.ac.uk`; [2 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.webfeat.lib.ed.ac.uk)

Typically the rewrite would look like this:

 * http://www.ams.org.proxy.library.adelaide.edu.au/mathscinet-getitem?mr=46042 $\to$ http://www.ams.org/mathscinet-getitem?mr=46042 (from [this answer](https://mathoverflow.net/revisions/273067/3))
 * http://www.numdam.org.proxy.library.cornell.edu/item?id=CM_1983__49_3_405_0 $\to$ http://www.numdam.org/item?id=CM_1983__49_3_405_0 (from [this question](https://mathoverflow.net/revisions/183160/4))
 * http://ezproxy.library.nyu.edu:2233/mathscinet-getitem?mr=1042048 $\to$ http://www.ams.org/mathscinet-getitem?mr=1042048 (from [this answer](https://mathoverflow.net/revisions/167652/2))
 * http://www.jstor.org.libproxy.smith.edu:2048/stable/2031721 $\to$ http://www.jstor.org/stable/2031721 (from [this question](https://mathoverflow.net/revisions/218884/3))

Some differently looking changes:

 * https://doi-org.proxy.library.nd.edu/10.1016/S0022-4049(02)00126-3 $\to$ https://doi.org/10.1016/S0022-4049(02)00126-3 (from [this answer](https://mathoverflow.net/revisions/289132/1))