Trams are not some magical tech that is uniquely immune to manufacturer lock in.
No, they're indeed not magical. However they
are completely immune to manufacturer lock-in, because the basic principles of them are not under patent. They are also well-tested, reliable, widespread and well-understood.
I just don't
get rubber tyred metros other than in extreme cases like Lausanne where it was that or a rack railway/funicular due to the extreme gradient. They don't appear to have any advantage whatsoever and a
lot of disadvantages. According to Wiki, there are just 8 systems worldwide. How many tramways are there again?
As for CBTC (Communications-based train control) isn't ETCS a standard, thus you can get your kit from any manufacturer? Though TBH I can't really see why a conventional tram with a squishy thing in the front seat would not work in this context. Just put some of it in tunnel (see Den Haag) if that is necessary.
Just build a tramway. It is the obvious, practical, inexpensive, standardised, off-the-shelf, extensible option. If you need to stick some of it in a tunnel, do so, building the tunnel based on existing, well-established road/rail tunnelling practice.