I am guessing the additional signalling costs may make the ramped bridge still cheaper but with in cab signalling........
A Penryn Loop actually can save a signal versus a conventional configuration using colour lights because the bypass loop doesn't need a signal on it at all. See my animation here:
https://youtu.be/1H9EV0iT0dQ
Whatever the track layout, there's no point in trying to avoid colour light signalling with some kind of token and stop-board lash-up. Apart from tokens being slow to exchange, the old hydropneumatic train operated points used originally on Central Wales NSTR, and RETB lines in the Highlands etc, are no longer available and they've all been converted to conventional point machines with local train detection and interlocking logic to command them and prevent them motoring under a train. They also need 'point indicators' for both facing and trailing moves that look remarkably like colour light signals! Add to that the requirement for TPWS at the stop boards (with an indicator) and today such an arrangement will likely cost no less than a modular TCB arrangement using the modern lightweight fold-down LED signals and axle counters for the local train detection and long single line block sections.
Cab signalling? Yes great but you still need train detection, point actuation, interlocking logic and a control centre. The ETCS pilot on Cambrian certainly demonstrated no economies over conventional TCB (both using axle counters). The latter has got cheaper, easier and quicker to engineer using the modular concept including the new signals.
For the vertically integrated Island Line there is a unique opportunity to control the whole simplified line from a workstation at (say) Ryde Esplanade station which could incorporate automation for normal working and be supervised by someone from the company (suitably trained as a signaller of course) who also had other duties such as running the ticket office or supervising train crew.
