What happens if FC get relegated and the academy get promoted? Not beyond the realms of possibility at present given how poor FC are the past seven years. Would we play each other?

I reckon they'd only scrap it if they found out it was going to cost them too much money. That seems to be the basis for decision making at the clubs now.
That said, Rovers vote for the marquee rule and then scrap their academy to jump on the back of ours.
Had faith in AP , but that's gone now.

Too blooming right we'll probably draw the new merged team in the Cup and they'll beat us! Hull KR and Hull FC merged team in the top echilons of the RL is just something that has been delayed for 20 years, but always in mind, It's all back to the future ...18th April 1995 almost 100 years since the birth of the game the Rugby league stated, " 14 merged Clubs will contest the new league with the Hull one being known as Humberside" there's then name problem solved then!

Until today's HDM article I had not paid too much attention to this as I thought it's was merely an isolated cost cutting measure. Putting the team in the professional league structure has changed my opinion. Maybe it's a bit far fetched but I am concerned the RFL, AP and Hudgell are in cahoots to try and use this team to legitimise a unified Hull team playing in the professional league. We will then be presented with a doomsday scenario where both clubs are unsustainable and the only choice left is a full merger.
Call it a conspiracy theory if you like but I prefer to be cynical where the RFL are concerned.

Firstly you would need a fan base before that conspiracy theory would work , secondly you'll need a team of under 19s that are better than BOTH FC and KR and if the players are that good questions would be ask to why they are not signed up by either club in the draft system !!!
In a climate were crown figures are down who would go watch this new merged team ? We're would this team play ?

You misunderstood my point. It's not that the U19s would have to be competitive with the senior teams, they would just be used as an example of "everyone said it wouldn't work but here we are 2 years later and it's worked well".

Coupled with a load of "the clubs are unsustainable in their current format, it's either merge or both clubs go under" from Hudgell & Pearson, and the RFL promising the moon in assistance and it's not such a ridiculous scenario.