Interesting topic!
It seems Mahler won't be performed again for quite some time, besides his smaller works like lieder and, as you mentioned, arrangements and reductions.
Are you certain that Vänskä/Minnesota didn't capture any more recordings in their cycle beyond Mahler 10? They have 3, 8, and 9 left to go. I wonder if remote recording is off the table. I don't even know how it'd work.
Let's also not forget about the Ádám Fischer/Düsseldorf Mahler 2, probably coming out before the Mahler 6.
I'm also wondering about any Mahler recordings that were captured just before the outbreak. Will we perhaps see any more pop up from Roth/Gürzenich? Harding/Swedish Radio? Netopil/Essen? Gergiev/Munich? A Feltz Mahler 9? I feel like there were quite a few ongoing projects. I'd love to see the Alto label remaster the rest of the Gergiev/LSO cycle too. The 7 and 8 sound excellent.
In short, I think there's still more to come for a year or two, but there will definitely be an absence of Mahler symphonies for the foreseeable future. And to be frank, I'm kind of okay with it. I always love more Mahler, but we have a treasure trove to sift through.