Building out a full suite of FF lenses for a new proprietary mount would take a lot of capital, which I doubt they have. It makes more sense to me, if I were running OMDS to lean into my core competency in designing and building great lenses, than trying to compete with the big boys (who likely have deeper pockets) on their own
Even giant like Panasonic sold their entire semiconductor business including joint sensor company with Tower Jazz to Nuvoton so OMDS has flat zero resources to develop their own camera sensors which could compete against Sony.
For the very reason you mentioned, they also can't create their own FF or APS-C mount and cameras. Without full set of lenses new system would die instantly.
The only realistic option to do something else than m4/3 is to join L-mount alliance. OMDS could finally introduce that long-awaited PDAF-body and fill several gaps in L-mount lens portfolio making this time sure that everything includig AF, IS and weather sealing is 100% compatible between all L-mount models. Since L-mount has a decent lens portfolio, OMDS would only need to design a couple of Zuiko lenses to get started.
I believe there would still be a niche for compact and light stills-oriented nature photography body and a couple of high quality telephoto zooms and primes. This of course would be niche but still the same niche they already occupy in m4/3 and in L-mount it would certainly be "PRO" by anyones standards.