What locomotive would you most like to see in OO scale?

I think Hornby could do a later version of the P2 with the Bugatti streamlining as they already have the chassis.

I have long liked the idea of an A2/1 although there were but 4 of them.

Bachmann have the GCR D11 so a D10 should be quite easy

an N5 0-6-2tank how about Oxford for this one.

sensible choice, my layout is heavily GCR and freight so;

Bachmann an O4/8 there were 99 of these marriage of O4 chassis to 100A - O1 boiler

and for fun

GWR rebuilt MSWJunc no 16 2-6-0 only one of these but it once stood in for a failed King! the first one no 14 did not last long.

A Highland River 4-6-0 'cos I love these

The River still stands as my top choice, this (with a bit of brain power from Derby ) could have been the standard mixed traffic loco over 10 years before the Black 5 came along, still there has been progress, oddly 34c I have not seen a request for a J6 which I would have thought would have been up there, sorry if I missed it on your numerous postings.

I could start a thread on long lead times, I am still waiting for the new J39 which is odd as this was surely a well known and round about the system go anywhere freighter.
On the 9F side of things a rebuilt Crosti, now I saw these on the Colne Valley when a schoolboy so one I would fork out some beer tokens on especially as both big box makers have the chassis so surely not that difficult, they also actually lived quite a long time in this guise.

We (well at least 34c and I) are waiting for the Heljan O2/2 maybe one day perhaps it will hove to over the horizon. I agree to that an A5 and an N5 would both be welcome, I have these as kit built but they do devour maintenance. N1 would also be a nice addition just the thing for Halifax-Queensbury-Bradford service.

We now have the Q6 and there were quite a few similar freighters so a GCR Q4, GNR Q 123, LYR freighter and the LMS 7F are all possibles of course the GCR one is the most interesting/impressive of this bunch having outside cylinders

Now one loco that started out with an interesting career where the LYR rebuilt dreadnoughts, this should appeal to Scottish modellers as these worked the Preston-Glasgow section before the Scots, many withdrawn early until it was realised that the piston rings were rubbish and after adjustment the remaining few had quite a long life into BR days.

So maybe something to look forward to - eventually

PS I still like the A2/1 which is basically a V2 somewhat modified and of course that is another model rather overdue, announced prices leave me cold however so I may stick with the two I already have

The other change is that small batch manufacture is much easier these days so maybe back in 1960 Triang would release a model each year roughly, it was a major effort, sort of looked like a steamer but that was what there was, now we can knock out small volume highly accurate models costing reasonable numbers of beer tokens, so there is less impediment to making models of limited appeal, the trick is getting it right and this makes the market more interesting

So back to my ideas, Wolseley (perhaps an 18/85?) likes the totally useless but attractive 191 class, interesting that his ideas changed as soon as the Rivers turned up and later Caley locos looked like Rivers just they were naff, the 956 might have done OK but the Oban locos were really rubbish, I love the "wee contraption 'o' my ain" said Pickersgill when referring to the valve gear on the 956 but then perhaps there is enough volume to make a few sales and a few new manufacturers looking for a nice option no one else is looking at. (the 3 different Adams 4-4-2tanks case in point0

So I'll stick to the Rivers, A2/1, Q4, A5, N5, rebuilt Crosti 9F, 7F 0-8-0, etc

Yes 34c the desire for Thompson to make equal length conrods was behind those long front ends and Pepp simply crunched up the front end to make it look balanced but of course Pepp kept the 3 sets of valve gear that Thompson wanted and yes there was a lot right about the A1/A3/A10 and in this model the conjugated gear seemed to do better, but listen to one at speed and it sounds like a 4 cylinder loco with a missing cylinder and as I said above the V2 when put on the test plant showed it was not doing anything in one direction. So technically Thompson was right to try and even up but not at the cost of the long front end, actually this is one of the reasons I like the A2/1 because the balance looks right. The other issue was the sheer size of the 50 sq ft grate which actually cost coal in order to keep the grate covered. so again the A2/1 with the smaller grate looks right and they could run at very small cut offs, were fast and pulled well, shame there were only 4 of them.
On one point somewhat to my surprise the original A1 was no better in use than the Raven A2 again one suspects the conjugated gear did the A1 no favours whilst the A2 was sound it just looked antideluvian.

So I can add the A2/1 to my list

The other quite interesting effort was the V4, only 2 of them of course, I have one as a kit but a nice manufacturers model would be a nice effort, complicated and expensive as it was the B1 was clearly better in every regard but who knows we might have had a few hundred V4's.