I can't see the point. Look at the losses and gains:
Gain: prevents a *tiny* amount of spamming (tiny, because the average lifespan of linkspam on the 'pedia is maybe 2 minutes - our editors watch this stuff like hawks.
Loss:
(1) extra complication to the code. (Small and slim is *always* best.) (2) even more crud to mess up the HTML output. If we keep on adding "features" in this manner, a page of MediaWiki output HTML is going to be harder to read and consume more bandwidth than a page produced by Frontpage.
To me, that says that, on balance, the best option is fairly clearly to do nothing.
Small is beautiful. Simple is best.