It's been a while since I've been on here and since then I've actually had the opportunity to explore some non-London buses.
I'm now quite partial to the buses of Hertfordshire (I do like Hertfordshire V4), but specifically as a pipedream would love a Hemel Hempstead route. The old 500 route, or the new 508 would be a dream. Unlike the London ones I mentioned last year I'm pretty sure almost if not all the buses in recent times that were on the old 500 and now the 508 are already represented in OMSI.