Statehood vote only requires a simple majority vote in Congress, meaning 51 votes in the Senate. Of course there is the requirement of 60 votes to shut down a Senate filibuster, but that is an internal Senate rule and it only requires 51 votes to abolish the filibuster for statehood.
I think Senate Dems in swing states will be very leery of statehood for DC, but it is a real possibility.
Actually Dems could grant statehood to Puerto Rico, the Virgin Islands, Guam and any other territory or locale with a simple majority vote in Congress. Talk about a requirement of a 3/4 majority in Congress or Constitutional Amendments is just wrong, granting statehood is very simple, the major exception being you can’t carve new states out of an existing state (meaning no new states from California for example). Dems could easily separate out a portion of DC from Capitol Hill, the White House etc and grant statehood.
Area-wise, the Upper Peninsula of Michigan could become a new state, but it doesn't have many people (the largest cities seem to be in the 10,000 to 25,000 range), and it might be forbidden by the Northwest Ordinance which foresaw creating no more than 5 states in the Northwest Territory...if that would still apply. But it might provide two Republican senators. Could call it Superior after Lake Superior.