Bloodyhell - that's a hard one....
I would say something like £1.5 billion factors in the anticipated 'known' revenues (stadium, extra events, NFL, potential for a realistic naming rights deal, current broadcasting revenue and recent trends along with our £1.4b+ of gross debt) with there being a fair amount of padding there for the potential of increased revenue from streaming/social media monetisation.
Quite telling that Daniel Ek's bid for Arsenal was £1.8 billion (similar sized stadium, similar revenues, larger current fan base, a (seemingly) more prestigious asset, and vastly lower gross debt than THFC). Though it is also telling that Kroenke rejected this offer out of hand. I think at present PL club owners think the streaming/social media revenue will be huge in (say) a decade's time. In the interim I think sales of football clubs are only likely to occur if owners get into money trouble. Though once the promised land of streaming/social media revenue arrives I still don't really see how owners can make a profit out of running a club (other than through selling up and realising the asset price increase) as clubs would still need to be operating near the top of the pile to gain/maintain fan interest and that will see the clubs competing with each other by spending more and more money on transfer fees and wages.
Of course the key to any good investment is knowing when to get in and when to get out. ENIC certainly got in at a good time. I'm sure they will get out at a good time as well, they are run by very clever men. My thoughts are that somewhere around the 5th year of large growth in streaming revenues might be the sweet spot here. The potential of this growing forever will still be priced into the asset values and the transfer fees and wages may not have initially kept pace with that steep growth. As the revenue growth starts to slow and the fees and wages catch up then we may start to see the trend slowing and the same level of upside is unlikely to be priced in. That's just my opinion though, it could be that this revenue stream is still growing at a massive rate a decade or more after it initially booms or that something completely new comes along that we haven't even considered yet that blows existing revenue streams out of the water. There is also the fact that the World's population is growing at a fast rate and the World is becoming a smaller place so that clubs can attract far flung fans on a much wider scale (as things like streaming and social media will hugely enable, especially with the ability to get online improving in every single far-flung corner of the World).
I actually tried to put a consortium together to buy Leeds many years ago. I thought that football as an entertainment business was still vastly undervalued and the upside for a reasonably big one club city was large. I hadn't factored in the potential for streaming and the World becoming smaller back then and couldn't raise enough capital from private investors to make a go of it. I think if I had considered that and made it part of the pitch then I may well be sitting here today running Leeds, almost as rich as Daniel Levy.... Oh for a time machine!... Though I'd probably have a bunch of Leeds fans griping about how much I had got wrong at the club just as happens on here with Levy.