Even easier to just let people with limited mobility board at Central. I presume the trains will still be making a call there for people who are changing, just as they call at Queen Street when it's "closed".
I was handed a little booklet yesterday at Queen Street station explaining the arrangements for today, and indeed those with "accessibilty requirements" are invited to use either station. It also says that (now anyway) on the web site referred to above.
The problem with lack of queuing space outside Queen Street appears to have been addressed by adding queuing capacity on the platforms and using platform 2 for all Southbound services.
The diagram makes it look as if platform 3 is used for Aberdare services but I don't think that's possible.
No suggestion of what someone for Cardiff Bay would do but then on previous occasions using the Bay line from Queen Street wasn't very practical as it would presumably have involved walking to Central, queuing, then changing at Queen Street.
In a nice sign of joined up thinking the final page tells you where to catch your bus from if you don't fancy queuing for a train.
There is a list of destinations on the web site to be served by Queen Street not Central and it doesn't seem to include Cardiff Bay so I'm not sure what the plan is, other than perhaps it's quicker for most people just to walk than queue to use the train.
Incidentally the whole change seems to be not because the area they previous used is currently unavailable due to construction works, but that it will be and they want to try things out now, and with hints that overall it's a better scheme anyway - they say this means they can increase the number of queues from 3 to 9 so that fewer destinations share a queue though I'm not sure quite how that works.