They definitely can do a lot of 80s/90s stories.
I slept on this thought, but if the original team is brought back and doesn't want to do the marriage years, there's a good chance that that alone kills Spider-Man '98 with fans. Especially in this climate. You have entire generations of fans who grew up with the marriage now, hate for OMD seems to be at an all time high, and the new Ultimate Spider-Man is killing it partly because it's finally giving people what they want.
Add to that that the marriage is the clearly the obvious next step in that continuity (Peter and MJ are still legally married like you said plus the last scene in TAS is Peter telling Stan Lee "We all have to grow up, even us fictional characters" lol), and I think any attempt to string Peter and MJ along will be seen as artificial interference from the writers. Kinda like how Wells breaking them up after Spencer was seen as artificial interference and immediately rejected. And I don't think Feige wants to bring all that debate and controversy to a Disney+ project. It just seems like a bad PR move. So I imagine that being against Peter and MJ getting married would be an immediate disqualification from working on Spider-Man '98.