I completely agree here. The big point for me here is that changing the middleware without consideration of the current app-layer, as you described - adds significant cost to projects already using SLP.
This is easy to disregard if you are just focused on drawing board projects that may be possible after SLP v2 (or whatever else) reaches consensus and launches next year after May 2022, or you don’t consider the fact that businesses have to spend/hire dev time to write new code whenever the backend requirements change significantly.
Imagine having to get Tether to reimplement the whole thing again on a new system, completely changing the APIs and libraries. Imagine not supporting SLP v1 and just deprecating it without a migration plan.
What would that say to businesses and users who have already invested money and time in SLP? Disregarding this is easy if you are excited by the new shiny thing, and there is no cost to you to drop legacy support for existing users.
The key certainly is to not affect the app-layer at all, and ideally almost zero cost to current SLP projects, and not do this by breaking all the wallets that currently rely on SLP v1 middleware. A community-supported migration plan is a must.
It is also unreasonable to drop support for SLP v1, simply because something is coming in May 2022, which frankly to businesses is very far away right now. Unless you want them to incentivize them to leave in the meantime.
(There is also a small small chance that no superior token solution will reach production or get adopted, let’s say smartbch is filled with problems, in that case you still want current SLP to fall back on, as many challenges and issues it does have at the moment, it is still a solution for token issuers. Therefore, it makes zero sense to me why advocates of successor proposals constantly want SLP v1 support to be dropped/deprecated immedietely.)
I think I should also state the pragmatic reality, we all know to be true here - that BCH devs are not exactly teeming with extra time to rewrite their software from ground up.