As I understand it, the FAA would not issue an AD for SLSAs because of an engine issue. Rotax would be the one to do that, in the form of a mandatory service bulletin.
SLSAs, under the regs, are required be maintained in accordance with the manufacturer's directives, and that includes compliance with mandatory SBs from airframe, engine, and propeller manufacturer. To my knowledge, every SLSA basically "punts" the engine maintenance to the engine manufacturer (predominantly Rotax on SLSA), requiring the owner to maintain the engine in accordance with Rotax guidance.
And Rotax seems to be considerably more strict than the FAA when it comes to those mandatory service bulletins, service intervals (5-year flexible hose replacements), and even overhaul schedules (calendar expiration is enforced, regardless of the engine time). There are plenty of Rotax 912ULS engines sold to experimental builders because they hit the calendar date for overhaul while still well below the TBO in hours, and the SLSA owner realized they could sell their current engine for enough money that they put that money towards a new engine at basically the same out of pocket cost as a complete overhaul at one of the factory-authorized overhaul facilities. (Experimental aircraft, of course, don't have to comply with "mandatory" service bulletins, and those Rotax 912 engines are pretty daggone reliable, even with higher hours.)
That requirement to maintain the aircraft per the manufacturer's guidance presents a unique challenge when it comes to "upgrades" for SLSA. Even something as simple as swapping out an old Dynon screen for one of the new HDX screens would require an "approval letter", unless the manufacturer listed the HDX on their approved equipment list. Hard to get that if you happen to own an SLSA whose manufacturer is out of business... The only solution for those "out of business" folks is to move the airplane to the Experimental category by converting them to E-LSA.