And I'll add that there's another axis: gwicke (and others?) have been arguing for a broader "collection of services" architecture for mw. This would decouple some of the installability issues. Even if PDF rendering (say) was a huge monster, Jimmy MediaWiki might still be able to simply install the core of the system. Slow progress making PDF rendering "more friendly" wouldn't need to hamper all the Jane MediaWikis who don't need that feature.
These issues cross-couple. Making a really super-easy "giant VM blob" that contained an entire complicated MediaWiki setup with all bells and whistles might as a side-effect make it less pressing to decouple the services and simplify the installation -- so long as the giant blob worked, no one needs to know what darkness lay beneath the hood. (Is that a good or a bad thing?) Conversely, making 'apt-get install mediawiki mediawiki-pdf' Just Work would make it less relevant whether 'mediawiki-pdf' was a separate service or a tightly-coupled mediawiki extension.
In practice, what is needed most are people to actually work on making the process friendly, one way or another. (I've done my part by aggressively patching extension READMEs as I come across them to keep them up to date and accurate.) --scott