Property will flatline or possibly move slightly up for the majority of the country. It won't collapse because the need for accommodation is too great. Ignore central London which is in a parallel universe and reliant on the whims of the very rich. There is sufficient money that needs laundering to keep the top end property market buoyant for years. All that QE and bribery has to find a home somewhere.
Collectibles are where they always were. The best and the rest. The top pieces always command top dollar, but the pressure is on the also rans. It has become progressivly difficult to sell lower grade items for a good price (obviously with exceptions) as the internet has opened up new sources of material to the average collector. You are no longer restricted to a handful of shops in your local area plus Spink and Seaby if you subscribed. The world has always had more material available than collectors to buy it. More people are doing background work to seek out the more desirable piecces, essentially driven by computer databases. This keeps specialist areas buoyant.
A lot of people jumped on the collectibles bandwagon when interest rates dropped to zero or thereabouts. In some cases this was not a question of making money, rather preserving it by diversification. The first real test of the market's resilience will be when interest rates creep back up again, as this will ask questions of those who diversified for reasons other than they like coins. I think the market has been moving slightly downhill for 'average' pieces for a while, but it depends on the mood on the day. A lack of fresh material will constrain prices, but a collection that has been off the market for half a century will usually do very well - think Marshall, Slaney, Boyd and a couple others.
I don't think the market is likely to collapse given the level of disposable income and the changes in society mentality. A generation ago people saved up for a house. Today, a large number of people are unwilling to do this, preferring to spend their disposable income. It doesn't require a large number of people to take up numismatics to distort the markets given we are regularly talking about the number of examples of this that and the other that are available.
With collectibles, the only important question in determining the trend is how much would it realise if I sold it today? People pay as much or as little as they feel necessary to obtain something, but I guarantee they want to sell for the most they can get, unless a forced seller.