I think Gloucestershire Airport could make an excellent schedule/charter airfield with the appropriate business plan. If you look at around at the local business in the Area i.e. GCHQ, QinetiQ DSTL etc where regular quantities of staff make frequent trips to London (£100 on the train) and Europe there is some scope for revenue from excesses of government money spent on travel. I think the main stumbling block is the issue of the runway extension which there is very little commitment too and apparently provides a 'W' take off limitation for anything of SD360 size and above.
As for accessibility I do not know of many airports in such close proximation of a major motorway.
cheers
MJR