They still make money off of the GOG Six-Pack and that might reduce what little they make from it. In return, I have one question for you, what do they have to gain from this from a business standpoint?
I don't think they would lose the very minimal sales m&m six pack is giving for such a big company like Ubi. Also, I think IMHO most of the purchases is from people wanting the VI part (or even WoX). I don't think M&M 1 would sell if it would be offered apart as a single game.
Regarding what they have to gain... think about good press, prestige... SMART MARKETING move. That's what companies pursue when open source any of their assets or when release publicly some ancient software (see Microsoft, for example). I think Ubisoft would obtain a good image if GOG includes M&M1 in their catalog of free games every customer has im their game library, jist amomg the Ultima titles or Akalabeth.
About the remakes... think of an engine like Dark Mesiah but maintaning the essence and playability (even turn based) of M&M1... For example, I think ID software made a good job in the recent Doom remake. It's the same fast paced action experience than the original Doom, but with current technology steroids!
But I"m going off focus of my original post... what I would like is to see, appreciate, enjoy and learn reading a piece of historical code (three years/one man!). Not the code from the DOS version but for such an ancient machine as an Apple II... From my point of view, nothing to lose from Ubi/JVC and much to gain in reputation/publicity (think in the game news worldwide publishing the news of the release of the "mythical" original source code of M&M)