I do attend the progress meetings at Transport Scotland.
The introduction is likely to be on one route at a time, so that gauging (153's are not quite the same as 156's) and stabling - initially 2 units operating with 1 maintenance/spare can be at one location. This will probably be Glasgow-Oban
The real challenge is that the most popular train is the 08.21 on a Saturday - connecting with the key ferry services to the outer isles, and other Argyll cycle tours. This is a splitter 2 to Oban 2 for Fort Bill 2 for Mallaig. last time I checked one out all bike spaces to Oban booked, 9 spaces available in other carriages. I've been directing disappointed cyclists to Buchanan Bus Station, where they can catch the Citylink 976 with their bikes (officially in bags) at 08.30/09.00 winter/summer. The summer 06.15 coach makes a handy connection for the overnight sleeper either in Glasgow (approx 30 min) or at Arrochar (approx 10 min)
One problem is that the length limit for these trains is (currently) 6 coaches, so the addition of a 153 to the most popular train in current timetable might not be possible.