Basically, we have 10-20+ years that we need to look at when we are talking about long term and not just short term. In that case I would assume that the most logical situation probably would be just hoping that the casino you picked can go along the furthest compared to other places, and just do not deposit a lot like you said. There are people who wager with millions but I am pretty sure they have more than enough even if they lose that.
" if they are offered. And even small amounts will not be bet. But it's true, who knows what will happen in 10-20 years 
It's kind of reminiscent of long-term government bonds. Someone is in fact and buys them.
So probably some individual people will be found - and will play on such a long-term dispute. This site may find them, but there are too few of them.
If they would offer more lines or markets but I don't see for it to be having any changes in terms of demand and interest.This is already the sad fact that this site
isn't really much that really appealing on knowing your bet outcome for months or years to come.
The first worry of those bettors who will bet on the line for long term is, will the site be still up and running during that period? As we have no idea about the long term plans of the site, you are just trusting that every bet you make, the site will still be there and will have no problem if in case you need to cash out. The team here seems not aggressive in terms of promoting their site, so maybe this is just a side project of them.
be still existing on that particular time and able to pay up those bettors who had won?
Cant be sure on what would happen ahead on the site and its one of the reason on why people are dubious on betting because they don't know on how long they would last in the market.