Yes it would. Unfortunately, I seem to recall there is a requirement for self-power functionality for more off-wire services so energy efficient electric IC225s are to be replaced by something lugging around lots of batteries and/or diesel engines.
Given the issues of maintainance for micro-fleets, I think GBR needs to create a shared InterCity fleet for all the main lines. For example, rather than EMR, XC and LNER each having their own bi-mode fleets for their off-wire services (eg. summer extras to Skegness and St. Pancras to Lincoln for EMR) just have a common pool of bi-mode units maintained together for all three TOCs to use as required (particularly since EMR will have hardly any off-wire services once the wires get to Sheffield and Nottingham so would be running bi-modes under the wires most of the day just for the odd Lincoln, Melton Mowbray and Skegness services). Wires to Oxford, Bristol and Swansea would allow GWR to bring in some electric stock and release some bi-modes, although it might make more sense for XC to have those bi-modes as one of the Agility (Hitachi) depots that maintains those bi-modes is conveniently located for XC services (near Bristol Parkway).
I think you are both forgetting that the class 801s already have a diesel genset under one of the coaches (possibly even two of the coaches on the 9-car 801s, but I'm not sure about that). I know the class 801s are missleadingly called EMUs by some sources (even highly respected ones) and from an operational point of view they are but from a technical point of view they are bi-modes. I do wonder whether it would be feesible to shuffle either gensets or the genset vehicles (complete with genset) between units to create some true EMUs (with no gensets at all) and more full-spec class 800/802 bi-modes (with several gensets).
I'm pretty sure it was not just 'intended to go 140mph' but actually did for a time.
http://www.traintesting.com/ic225_5.htm states that "the line speed between Peterborough and Grantham was increased to 140 mile/h to allow the 91's to show their paces" and "Many was the time we had to brake for the last curve in the Down direction (uphill) which had a 135 mile/h restriction". The way I understand it, the author is referring to a full change to the linespeed, not just specially authorised test runs, given he also says "We also undertook a few demonstration runs when we ran at 140 mile/h, where the line speed was 125 mile/h, all the way from KX to Edinburgh arriving there in the record time of three and a half hours!" which strongly implies that they were specifically authorised to exceed the 125mph linespeed in certain cases but also were able to run at 140mph on limited sections without such authorisation. This is also supported by the fact that
there is a 140mph linespeed sign in the National Railway Museum. Of course, the linespeed
may have been cut to 125mph before the IC225s entered passenger service but if so it is just unhappy chance that they never did 140mph in service.
Presumably the higher level of maintainance necessary to exceed 125mph has not been maintained however and you would not be able to do so now without increasing maintainance accordingly.