Yes, some are likely to be hard to reproduce since "vanilla" sources aren't available, but the concept of actually porting it (with the experience of using it) "as is" is superb. Once it's pretty much done people could work on variants, like one that doesn't really have some bugs and limits but warns about them or one that's pretty much the same but adds some sort of mass multi-player functionality, or people could take some chocolate implementations and somehow enhance old school engines with the information. The bugs and limitations should include things like flat and sprite loading, as these affect the way maps are made for "vanilla." But the thing would be "first get it ported, then play around."
What I'd like to see is full implementation of all the Doom 1.9 limitations and bugs (even and especially the ones that cause the game to crash).
To illustrate the effect of a bug to the user, let's take the VPO itself; and let's say you are recording. The VPO becomes part of the map in such a way that you either avoid triggering the VPO, or your demo is eliminated. The complete impossibility to record while viewing too many visplanes makes up part of the experience of playing (and recording) or editing for "vanilla." If you start to mess with some bugs you start to change the way it can be used (which includes that it can't.)
This is another feature a variant could well have, but 640x400 is proper as things go (a decent res already, akin to Doom95's hi res and on the same exact ratio as Doom.) I mean, PrBoom-plus already has these features, and it can even record v1.9 demos. Implementing every kinky feature someone requests would mong up the product. Why hi res and not hi frequency sounds or MP3 music? All that deviates the project from its purpose and is already possible with the plethora of engines available. Plus the source is available and anyone can add stuff. But would that be chocolate? Maybe swiss chocolate or chocolate with nuts.
What I'd also like to see is support for high resolutions and uncapped FPS (of course only as options and not as the default setting).
Chocolate Doom seems to be going great as of now, and some of the things already implemented surprised me and are in my opinion crucial to the user-wise "as is" concept, like a novert option and mouse acceleration, as they came with DOS, easily thus getting into Doom, and the way it can work and has often been used. Also the use of exact CFGs plus an additional for special settings was also on target.
The next big step would appear to be DeHackEd support, which has never been fully implemented in any other engines, as far as I know. BEX expands it and is also unable to take some text-based input, like some resource names, for example. Even such things as the -file warning text should be supported (some add-ons use it to say something about the changes or the wad, for instance.)
Eventually there's also MultiPlayer. The standard methods should be kept: IPX; 4 Player LAN, 2 Player serial, and even modem to modem (it may seem ancient, but still useful for people without high speed Internet or people with flat phone bills and a spare dial-up modem.) Additionally TCP/IP otherwise working like LAN would be great, to function like Doom over Kahn, Kali, Git or the former MS Zone, especially since IPX is rather deprecated for today's systems.