This question has been asked a few times → if there will be an enable/disable switch on the new SL plugin like there are with Routines. At this point it is unknown but we will find out once ST releases the new SL plugin.
More unknowns until they release it. Will it be the same as the old SL with all the current features or will it be a new SL will a different set of features but missing some that are currently available?? Will be interesting to see what they release.
Depending on how you set up your seasonal adjustments, you can probably use the custom Vcalendar and Automations to do some of what you want.