New Fleet will work on short-haul and long-haul and will have radically different working practices to the current LHR fleets. They will basically work to the CAA guidelines and that's it. No payments for working one-down. No restrictive disruption agreement. No seniority. And so it goes on. Pay and promotion will be linked to performance.
To get the full efficiency from the new T&Cs for crew, they have to work separately from the existing fleets.
New Fleet is a threat, partly because the current routes are divided between "money" (HKG, SIN, NRT etc) and "charity" trips (India, Africa). The former destinations pay absurdly high allowances. On the latter, some crew think they are doing the company and pax a favour by turning up to work.
If CC were paid an hourly rate for the work they did, New Fleet wouldn't be such a threat. This was actually proposed by the company a couple of years ago, but BASSA wouldn't entertain the idea.
Personally, I don't think that New Fleet will be mean that current crew will be starved of work.
What it will mean is that the days when BASSA was able to call the shots at LHR and dictate the operation are over. Over time, the current LHR fleets will have to accept gradual changes to working practices, because their inefficiency will be laid bare when New Fleet is up and running.