You will have the blockchain slowly.

Frankly, I don't see much use in blockchains besides public verifiable high-importance transactions where a significant number of parties does not trust each other, and some may be actively subversive. That is, a public ledger.

For less public cases, mere encryption could suffice, which is much faster. Most communications are between only two parties; they can check each other's key fingerprint via phone or a third party they both trust, if they even bother.

You'll have a blockchain, but the outstanding majority of blocks will be orphans and thus lost and invalid. Lots of promises will be broken.

You'll only know a transaction was confirmed after many months -- and before you get a confirmed transaction you may have to issue the same transaction hundreds of times.