Given that 222s have run in 4, 5, 7, 8 and 9 car formations, surely it must be relatively easy to make, for example, a 6 car 8xx? Not saying that EMR should get a train of that length, of course; but the principle of constructing X number of cars shouldn’t be that much harder to do.
I think that the 810 order being a mix of 5 and 10 (like 810/0 and 810/1) could have been good - a decent number of services will have sufficient demand for 10-car running; and 10 car units would have made more efficient use of space (two driving cabs and noses less) and easier in terms of staffing. But it is what it is - let’s hope that the 810 fleet lives up to the hype.
In any case, it was good to see 810003 make an appearance in a recent YouTube video. Hopefully the ball starts rolling a little quicker and full entry into service will stay at December 2025 - it would be completely and utterly unacceptable if this runs into 2026.