Separate check-in would be a great bonus. In fact, if it's too expensive to have a dedicated WT+ check-in for the small number of WT+ pax (as W capacity is less than J capacity), J check-in privileges would add very little cost for huge "attraction" benefits.
In theory, Globaliser, what you say makes very good common-sense and would provide another plus point to the service.
The only trouble is, we've extended "F" Class check-in courtesies to Gold and One-World Emerald card-holders (which, looking at the current EC promotion, now includes Star Alliance equivalent card-holders!), and "J" class check-in for Silver and OW Sapphires. At certain times of day, the queues for "Premier" check-in are longer than for bog-standard Economy! This then means that when Lord Reginald Fortescue-Smythe III makes his entrance with his £5000 First Class ticket, he waits behind Mum Dad and Aunty Flo who are "friends" of a Gold card holder (not strictly above-board, but you wouldn't believe how many try to use this approach!!!)
However, to mark up a couple of desks as "World Traveller Plus" and put a small rope queue in front of them wouldn't break the bank and, when there are no WT+ customers waiting, the staff could supplement the main Economy desks. Why haven't BA's marketing boys thought of this one???
atco-matic - re Lounge Access - I'm sure it wouldn't be difficult to estimate the likely lounge throughput in advance so that check-in could advise WT+ whether or not it is available for a small charge. LHR is probably too busy (now that all the One World cardholders are added to the equation, but I'm sure something could be made to work at LGW. It's something Bluejay or myself could mention if we are ever able to get to a Forum with our management!