Interesting point, so in theory you could have 1 x 8-car tph calling at those stations only (to shift the RDG-GTW market swiftly), closely followed by 1 x 4-car tph all stations. As with an earlier timetable the fast would catch up the previous slow to give a roughly 30-30 headway at Guildford in each direction. Not ideal, but then tweak this with selective SDO and/or platform lengthening at a couple of stations, to cope with, say, peak movements and you could increase overall capacity considerably within the 2tph limit, assuming that this would even be required over 2tph 4-car bemus on roughly the present service pattern.
You could even add a 3rd tph Reading to Guildford slow/semi-fast, this section almost level-crossing free (now Ash has gone) and with signalling capacity (I believe, as XC used to use it), as this is the busier end of the line if you subtract the Gatwick movement, and more likely to develop in its own right.