I wouldn't worry about this. Remember, Dropbox and many other apps not yet converted "just work" as they always have. By the time that Rosetta 2 is no more, those that find the Mac segment profitable enough will have converted their apps. Those that don't, won't.
By that time, you'll probably be on your next M-series Mac and you can keep the old one around for Rosetta 2 needs. Again, I've still got a Snow Leopard Mac running for Rosetta 1 needs for apps that never converted.
This is likely just business. Mac Silicon is the future but the bulk of the Mac market is still Intel Macs. Rosetta lets just about everything that works on Intel work on Silicon. So companies can take their time evolving their apps while Rosetta 2 is available. Looking back at the Rosetta 1 transition, they have upwards of a few YEARS before they need to either work natively or not. I doubt something as important as Dropbox won't be there long before it gets to that. If they do as their leader said in the Tweet and roll out native in Q1, they will have likely beat the BULK of all such developers to being native.
Looking back at Rosetta 1, the biggest casualty will be some favorite games that have already made the bulk of their money. Some of them will definitely NOT be evolved. So if you have some favorites that seem to be towards the end of their popularity (as in new sales) cycle, plan to keep a Mac with Rosetta 2 or hang on to at least 1 Intel Mac.