This is, naturally, awesome.
If I put my backseat driving hat on :D my next steps would be to
a) Wait for things to take off, iron out the initial kinks, and become quietly successful, then talk to the city at a few levels higher to showcase the benefits of cohesive open data, or at least structured data - leading the conversation here might (?) be interesting, but fostering additional connectivity between different branches (while helping to frame the focal points of the technical discussion, which is critical yet often tricky) would leave a positive impression for starters, may also help with internal communication and efficiency, and will of course help everyone slowly lumber towards modernity overall.
b) Whisper "GTFS" in Google's ear ;)
I would definitely do (a) before (b) - particularly the slow-paced adoption and settlement process (maybe even quietly build the GTFS integration yourself, before making any noise) - to give the city the best fighting chance possible against involuntary infections of Chromebooks/Google Workspace/etc ;P around the time the GTFS people show up. Y'know, just in case. Good to have a position first and all that.
The reason (b) could be particularly interesting, is that - presuming there is currently poor or no integration (this suggestion is irrelevant otherwise) - running interference here successfully may (alongside improving transport info for everyone) wind up netting you an interesting position at the city (consistent, set for life, good opportunity for lateral movement and initiative-taking given your start point, etc) or a decent shot at whatever office/presence Google has in/near Slovenia (could be interesting, could be hit/miss, might not appeal at all).
It's entirely possible you're doing this because you're already in a solid position you're happy with, in which case ignore most of the above :D