I did look into whether 912's could be maintained per airswitched hours - the conclusion I arrived at, unfortunately, matches this view... https://foxbatpilot.com/2017/04/12/rotax-engines-4-scheduled-maintenance-update/ . Thanks to Peter Harlow who also corresponded with me via email. Key quote below.
So – make no mistake, if you have a 912-series Rotax engined aircraft, scheduled maintenance must be carried out based on engine running hours, NOT flight times!
On the topic of TBO, the advice was, from two sources, you must follow manufacturers rules to stay as LSA (either CASA or RAAus).. https://www.aopa.org/news-and-media/all-news/2016/april/pilot/pe_savvy Key quote below.
Here’s another oddity. Rotax also builds a certified 912S version for use in Normal-category airplanes such as the Liberty XL. When your certificated Rotax 912S reaches its 2,000-hour TBO, you can keep flying as long as the engine remains in airworthy condition, because TBOs are not compulsory for noncommercial operators of certificated aircraft. However, if you own a Van’s RV–12 SLSA powered by a Rotax 912ULS, you are required by regulation to overhaul it at the 2,000-hour mark—because that’s what Rotax says to do
Note: RAAus conversion from LSA to ELSA at TBO does however remain an option.