It's a case of a damned if you do, damned if you don't, for the campaign and MP.
If they redesign the campaign, correcting what they consider flaws in the level design, an angry mob will descend on them because they skinned that holy cow. If they don't, other people will complain about repetitive levels and how they haven't aged well.
The MP is pretty much the same, either you're true to that unique, at times broken, feel no other Halo game has managed to recreate and you split your base down the middle or you just add maps to the Reach playlists and betray that game you're trying to celebrate.
At this point, in both cases, the best solution would be to go both ways.
Offer (in that new engine):
- to choose between a vanilla campaign and a "remastered" campaign
- to add the CE maps to existing Reach playlists and at the same time create new playlists dedicated to CE that accurately replicate the weapons and balance of CE
I'm pretty sure this won't happen but this would have been nice.
