One of the most important advantages of having this kind of project on blockchain is that you can have decentralised computer power and dont have to run internal servers which are a huge investment and use a lot of electricity and maintenance.
One of the downsides of having this kind of project on the blockchain is that transactions have to undergo a cumbersome ritual that doesn't scale. In other words, the decentralized computer isn't fast enough to deal with the apps running on it. As we can see from CryptoKitties. It's a trade off between performance and security (or is it trust?) and for some apps it doesn't make sense to run in the blockchain. Now if you were buying a Landrover thru Mark.space, sure, it's safer than sending a cheque by mail. But unfortunately you're sharing the decentralized computer with frivolous apps, so your payment fails or is delayed. Ethereum better solve this scalability problem soon because it's hurting business.
Have you even seen the roadmap? That stuff is a dang long way off, man! That lanky Ethereum guy said it's gonna take 3 years at least. Ain't nobody got time for that. That's a century in cryptotime. How's Mark.space going to be usable on this slow ass network? Who's going to wait 2 hours for the payment to come through in cyberspace?