I'm opposed to it primarily because a high speed train does not have corridor connections between the units.
"The train at platform 3 is for Caterham and Tattenham Corner. Join any part of he train for ... Purley Oaks and Purley, where the train will divide. Front four carriages for ... Whyteleafe, Whyltleafe South ... and Caterham. Rear 2 coaches for Reedham, Smitham, Wooemansterne, Tadworth and Tattenham Corner"
Amazing how the memory doesn't fade from childhood if you've heard something every day for years. Train was typically a 4 EPB and a 2 EPB unit, which were none-corridor and it seemed to work perfectly well.
"The train at platform 3 is for Worcester Foregate Street and Weymouth. Join any part of the train for Maidenhead, Twyford, Reading, Didcot and Swindon where the train will divide. Front 5 carriages for Kemble, Stroud, Stonehouse, Gloucester, Cheltenham Spa, Ashchurch, Worcester Shrub Hill and Worcester Foregate Street. Rear five carriages for Chippenham, Melksham, Trowbridge, Westbury, Frome, Bruton, Castle Cary, Yeovil Pen Mill, Maiden Newton, Dorchester South and Weymouth."
Far fetched? Every 2 hours, to comb in alterntately with local services on the Swindon - Westbury - Salisbury - Southampton run an local service on the Heart of Wessex, affording Westbury an hourly London service alternating via Swindon and via Newbury.
I have no objections to splitting none-gangwayed trains; seems a tiny price for making up a service that's got an appropriate length train for each sector, so becomes viable to run.
That is no different to having to change trains, I think Grahame can probably tell us how many passengers you lose by asking them to do that.
The figures I recall (not got data at hand) are 40% and 46% - one for leisure and one for commuter and business traffic. I forget which way round though!