For Padd - Plymouth / Penzance,
IEPs - unlikeley due to the expense
222s/221s - incredibly unlikeley as they will be near enough 20 years old, cramped, far less seating than at present (once a 1st class HST coach is converted to standard), lack the necessary luggage room and uncomfortable.
Why would the people of the west except "cast offs" from other routes, especially when they are unsuitable for the job?
So, I can imagine HSTs will be getting a life extension on this route for several years at least, and in my view that is most definitely the lesser of two evils.....
22x's could work, although it would mean that there would have to be a increase in frequency to accommodate the slight difference in seating (based on 2013 layouts of 222's and HST's). Although it is true that the HST's are seeing a reduction in the number of first class seats it would also be possible to reduce the number of first class seats on the 222's as well.
(2013 figures) FGW long distance HST (2+8) has 375 standard class and 112 or 118 first class (487/493 total seats), whilst the 5 coach 222's have 192 standard and 50 frst class and 10 tip up seats (252 total seats or 51% of the number of seats in an 8 coach IC125) whilst the 7 coach 222's have 236 standard class and 106 first class and 16 tip up seats (358 total seats or 72% of the number of seats in an 8 coach IC125). Either way for much of the year an adiquite amount of seating for most services.
However 2x5 coach 222's would have 504 seats (or slightly more than an IC125, but a few less at 484 if you do not count the tip up seats), whilst 7+4 coach 222's running togeter would have about 515 seats (again slightly more than an IC125, or 492 if you don't count the tip up seats).
All in all hardly far less than the current number of seats. They would also have the advantage that there could be direct trains to London from some of the branch lines in Cornwall (if there was sufficient demand) by splitting services. They would also speed up the services as not only would they be able to out accelerate the HST's but there could be a reduction in dwell time allowances due to not needing to worry about having doors left open.
IEP maybe perceived as expensive by some whilst others disagree (no point going over the arguments again here), however, if the trains to the west country are bi-modal sets which have been freed up by further electrification (i.e. extra EMU intercity trains) elsewhere then they could be useful rather than having to buy a new type of bi-modal or DMU intercity train.
The 222's could be a good stop gap until passenger numbers grow a bit more to justify the use of IEP and/or to allow time for electrification to free up IEP's. As the 5 coach bi-modal sets would bring many of the advantages of the options to split services, although the full length trains would have a higher capacity than the current HST's (about 18% more I believe).
