You can't viably operate an Embraer 190 into Heathrow. It's quite a noisy little thing and is charged as a "Super High" aircraft at £3,325 per landing AND per take-off at Heathrow. With 106 seats, you have a cost of £31.37 per passenger at 100% load factor just to pay the noise charge at Heathrow. In comparison, an A380 is a "Super Low" aircraft at £731.64 per movement so £1.55 per passenger at full load factor in BA configuration.
Any airline proposing to fly a 170 or 190 into Heathrow is either a) unaware of the charges or b) suicidal. The ATR72 is much better.
I'd very much doubt Loganair would be lining up for this unless the route is to be subsidised somehow. Of their Heathrow operations, Dundee and Derry are both PSOs and Isle of Man is apparently some type of PSO structure locally there. And I don't think JH had any personal issue at all with LBA - it was just that he couldn't see where you could make a profit flying from there, from what he had said. That presumably won't have changed?
The only practical answer here is that LBA is in discussions with BA again. They wouldn't be doing their jobs if they were not. It didn't do that well last time though - load factor in the mid 60%s range is nothing to write home about for using Heathrow slots unless there is an inordinately high value of connecting traffic in premium cabins.
BA does have a couple of European short-haul routes at LHR doing incredibly badly elsewhere and it might do better (read: less badly) flying those same slots and aircraft to LBA instead. It might lend a certain eau d'something to the equation. I'd therefore never say "never" but it's not massively exciting to say that LBA would be less bad than something else so let's have a go at flying it.