We asked GWR▸ quite early on whether it was possible to terminate local services at Bristol Parkway, and got a firm 'no'. I seem to remember the factors were junction capacity, platform capacity, and the undesirability of establishing a service pattern which would have to be unpicked when Brabazon and Henbury open.
It's not clear whether TfW's proposed half-hourly Cardiff - Bristol stoppers would call at Ashley Down - if they did, it would be transformative, leading to a proper 4 tph metro-style service when combined with the 2 tph Henburys.
GWR suggest Filton Abbey Wood as an interchange, although with 2 tph to BPW» and quite long connections it's not great; for example ASD - YAE gives journey times of around 40-50 mins, of which over half an hour is spent kicking your heals at FIT. Still quicker that the bus, but could be a lot better.
I think TFW will only run sn hourly service to Bristol
TM▸ along with an additional service to Gloucester as part of the proposals for. New local stations between Severn tunnel junction and Cardiff Central although I doubt we'll see all of them being built. Eg Llanwern or Magor I could only see one of them being constructed.
Ashley down is shown as a stop on the proposed Bristol TM service and I believe tfw are looking to order an additional batch of class 756s. Their level boarding will be a game changer for people in Bristol although curved platforms at Temple Meads will be interesting