In the Network Rail stations RUS http://preview.tinyurl.com/3uswno7 published yesterday, Bristol Parkway is one of eleven stations identified as at risk of overcrowding.
There is also a case study that discusses various measures that could be taken to alleviate overcrowding at Temple Meads - the most significant of these is the development of some of the Old Station area for booking offices and shops.
I think the latter would be a good idea since the station is situated in a retail desert and I'm sure many homecoming commuters would be glad of a Marks & Spencer where they could pick up a ready meal for the evening.
Overcrowding at Parkway and Temple Meads
Overcrowding at Parkway and Temple Meads
Andy Kirkham