There are huge cost and legal implications which will ultimately turn out to be prohibitive. Thats why studies failed last time. LHR considered the investment and logistics albeit on a much bigger scale and shied away.
Doubt for peak Jun to Sept at EDI this is in any way credible. DUB/SNN are historical legacy and now hard to withdraw, if was to be a new thing today, no way DUB/SNN would now have it.