...it's a shame and a waste that they aren't being used to their full capabilities.
I wonder, if the modifications being made to the GBRf ones prove to be a success, whether knowledge gained from that process might lead in the longer term to similar work being done on more of them, for use on duties other than the sleeper.
The 92s problem was (is) they were probably too complex for their own good - and to use them to those full capabilities was very costly and beset by problems. Added to that, the two main things they were built for either never happened (Nightstar European sleeper) or ever in the volumes anticipated (cross-channel freight).
With those not materialising, for someone like DB, it's a case of the costs of running them on 'internal' UK freight vs 90s, 66s etc. - all of which are cheaper and more reliable.
To answer your question, I think where GBRf are concerned there's potential for more use of the 92s. As it stands, they're the only A/C traction option they have and also the only loco capable of hauling the new sleeper stock, so GBRf (and Brush) have
had to sort them out.
Now they have some sort of 'formula' they're applying it to all 10 of the operational 92s they own (010/014/018/023/028/032/033/038/043/044). I understand six have been modified, one in progress (043) and three to go (032/038/044). These 10 are probably sufficient for current demand, roughly:
6 on Sleeper
2 on China Clay/Tunnel work (including Class 700 deliveries)
1 on Dagenham-Garston cars
1 'spare' (they're still 92s - there's always one needing some work!)
There's some talk of getting them back on some of the intermodals which are (mostly) under wires too in the longer term.
If GBRf were to win more business down the line they could use 92s on - and now they have a 'solution' - they might feasibly look to put back into service one or two more of the ones they have in store. Problem is most/all of these six have been sat outside to varying degrees for years and been parts donors to the ones that are working, so how many of them are viable or not is questionable. And logically each one further down the "queue of disrepair" becomes more and more costly to sort out, so comes a point fairly quickly it doesn't stack up. And at some stage, depending on what the work is, it's a better option to buy new rather than try and fix up an old loco which has had complex electronics rained on for a few years.
It's covered on this thread many posts ago, but as I understand it, 92020 and 92006 stored at Loughborough and the most likely (only?) candidates for getting operational again - although there's suggestions that at least 006 has some pretty bad corrosion.
92045/046 are sat in the Brush car park on blocks and no doubt liberated of many parts, so don't seem likely candidates for ever getting running again. And 021/040 are still over in Coquelles (Calais) where they've been sat (in the open I believe) for years - so who knows what state they're in!
As to whether DB would use the 'modifications' to get some of theirs going again - I really don't think so (see my response to InOban for a flavour of DB's approach to 92s). I think hell might just freeze over before they dug out any of their stored 92s (other than to send abroad).
The other option I've thought of is whether GBRf get to a point where they've got, say, the 11/12 back in service that they feasibly can, and they do want/need more - and some of DB's are in better nick than the remaining GBRf stored ones - would DB sell a couple to GBRf for them to do up? Again, I can't see this happening as DB seem to like to hang on to locos they have no use for and let them rust, rather than sell them to competitors to take business off them. Their stored 92s are all sat in the open too, so probably in no better condition either. That said, they've sold 60s and 67s to Colas, so who knows...
That would all be a long long way off though - for now, I think realistically we're looking at the 10 GBRf have in use - and if we're really lucky, one or two more. But that's it.