It's far simpler than SegWit, there's even less reason for controversy around it, and it won't be done using the BIP9 process which caused SegWit's unnecessary delays. I could see the Schnorr softfork completing next year.
Is the plan to implement Schnorr itself as one upgrade and leave the key aggregation part for a separate, later upgrade? I'm still not clear on that bit.
Also, will SIGHASH_NOINPUT and whichever other opcodes are needed for eltoo be included at the same time, or is that yet another softfork?
If I remember correctly satoshi used in the past softforks that didn't need mining signaling (basically a UASF? but there wasn't a name for it back then).
Yes, Satoshi always did UASF-style softforks.
That sounds like a bit of a stretch, IMO. Prior to SegWit, the network hadn't really experienced any controversies on that kind of scale when upgrading. UASF was considered revelatory (by some) as it was specifically designed to be implemented as:
"flag day activation" where nodes begin enforcement at a predetermined time in the future.
My understanding is that all the forks that occurred while satoshi was still around did not have a "flag day" (and were categorically not presented as an ultimatum to the miners). Arguably, the network has
never seen a UASF-style softfork. Although many believe the threat of one pressured miners into taking the action they did to activate SegWit.