The 108 is a though one. There's times when it's fairly empty and very busy. Unfortunately when the Jubilee Line runs into difficulties the 108 has to pay the debts of the Jubliee Line as it is the next most direct Link to North Greenwich.
I've said many times that the 108 needs 12 m Citaros on the next contract. I'm very glad that NX have finally decided to reduce the amount of LDPs on the 108, because they are totally inadequate the more standing space the better on the 108 I say.
Many of London's single decker routes are getting even busier. More recently the 132 had to be double decked to increase the capacity with existing PVLs which is a great thing, because it release a few more reliable DWLs from BX as many of NXs have in the past problems. I also think the 108 should be diverted to Stratford City this would save so much time on the route.
Routes in my area like 124, 178, 181, 225, 284, 202, 380, 484, P4 are becoming even busier day by day. 181, 284, 484 and P4 are sometimes busy end to end.
The other day a 484 was so busy 15 people had to wait for the next one. 10.8m buses would have been much better for this route!!!
The 380 now that it's using 10.2m darts is becoming even busier.
The only problem with the Citaros on the 108 might be that turn in East Greenwich, the DWLs often mount the kerb already. It could do with the capacity.
The 202 could be double-decked if there was will to do it. I hope some is found.
The 284 is getting a much needed capacity increase with the 10.8m Enviro200 - the interior layout is much more practical on them, too.
The 124 has tight turns, so only option there is a PVR increase.
The 225 could do with 10.8m buses but as it happens it's got perfectly adequate shorter LDPs. The ED workings on there are always welcome from my point of view.
The 484 should've got 10.2m buses when it went to Abellio, and it's a mystery why it didn't really - the capacity is much needed. 10.8m might be a bit tight, there's some fairly tight turns around Brockley - however, that shouldn't stop a 10.2m going round there and 10.2m LDPs used to do it.
The 380 got a much needed capacity increase with the Tempos and longer Darts.
The P4 has one tight turn at the bottom of Honor Oak Park (the road) where a longer bus might struggle (the Tempos don't seem to go out on the route) and there's also moaning Dulwich residents and low trees to prevent double deckers on the route. PVR increase is the main thing that will help with that route (and not putting flipping MPDs on there!)
The 178 is an odd route - at school times it's full to the brim with Thomas Tallis kids, and the rest of the day I've often been the only person on there. The B16 seems to have been route-tested to get DWLs round Kidbrooke (the tightest bit of the route AFAIK) so maybe 10.8m buses could be used - though that would obviously need route-testing. Other solution might be to schedule a couple of extra "schooldays only" buses in the morning and afternoon peaks.
SE London seems to have a lot of single-decker routes, and the majority of them can't have their capacity increased. Aside the ones you mentioned, a couple of others also sprung to mind:
The 42 - I'm personally hoping it's double-decked when the contract is up. Could use the capacity.
The 126 - Surprised the opportunity wasn't taken to double-deck it when the contract renewed. Could certainly use it sometimes - if the 261 has trouble it becomes packed to the brim from Grove Park to Bromley.
The 273 - Often packed to the brim by the third stop in Lewisham, and leaves people behind in Lee. Probably the problem is that it's pretty infrequent.