Does anyone know why 230001 is still using a class number applicable to Diesel electric traction? I know it’s a test unit at this stage, but if the trial is successful will the future permanent stock get a new number?
Probably because no-one has got round to changing it. There may be regulatory hoops to go through to introduce a new class. I understand that is why the re-engined class 73s didn't get a new classification (although most of them will rarely, if ever, operate off the live rail again). Normally such a drastic re-engineering would have done so (see classes 21/29, 30/31, 47/57, or 56/69).
Even quite minor engine/transmission variants used to mean a new class - see classes 08/10, 24/25, 26/27, 44/45/46, or 47/48.
Anyway, as a self-powered unit with electric transmission, one could argue it still fits in the 2xx range. If it is electric, it's a live rail one (like the 777s) so could be numbered in the 4xx or 5xx series - probably not the 7xx series as it could not be converted easily to take power from the overhead.