Is it at all possible that EMR are planning to do so at Leicester and St Pancras, maybe even Kettering, in due course? It might just be a case of limited resources to do it at all the stations at the same time. I have no evidence of that, just a passing thought.
I concur with those who suggested St Pancras is a bit limited for space to do such a thing, it's a busy place and taking up space for a seat trial would not go down too well!
I went to see the seats yesterday - there would be no shortage of room at St P to display what is on show - either on the ground level, the upper level or probably even on the small immediate EMR concourse - so it's probably down to station management - easier if it's an EMR managed station as said above.
So what of the seats themselves?
The display is 2 standard class seats side by side - so you can't get a sense of how close they will be to the opposite or the seats in front and thus a main comfort factor leg room. I found the seats pretty comfortable - but of course at most you prob sit in them for 5 mins at the display - not c1 hour like a trip would be.
I thought the vinyl or lether headrest area was good - easy to keep clean from dirty hair in these post anti Macassar days for a start. Similarly covered armrests seems a good idea.
Fabric on the seats (moquette) looks smart (moquette?) - it's 'ribbed' / textured as opposed to 'smooth' - this seems nice but I'd be unsure how easy it was to quickly keep clean - ie can you easily brush off crumbs etc on that finish. I'd assume that has been tested with cleaners input since making it easier to clean quickly saves money. But you can never be sure of such things.
So my view is that it's better than a Meridian seat, better than an Azuma seat and certainly better than a Thameslink seat. Not as good as the last generation of EMR HSTs (the ex LNER sets refurbished by VTEC)
No 1st class seats in the display.