Hi guys, just wanted to do a little update here from DatoCMS team!
We are perfectly aware of this limitation, and we think about it more or less every day 
We are just waiting for the right moment to deal with this, and I’d say that by the end of the year we should be able to close the matter once and for all.
We are still 100% convinced that blocks are a great thing, and we are proud to be one of the few CMS (or the only one?) to have a feature so powerful:
- Blocks allow you to create repeatable and reusable structures
- Blocks are 100% customizable
- Blocks do not count towards your plan records limit
- Blocks keep your project clean, avoiding orphaned records everywhere in your project
- Most importantly, on top of everything else, blocks keep content 100% structured (no random JSON, validations enforcement, possibility to reference other records/assets without workarounds, etc.). This means simple data migrations, data integrity and full control of your own content, which is what we care the most.
But… as @roger says, we also know that, without the possibility to nest them, it’s hard to decide if a “component” should be a model or a block. Even worse, a block may have to become a model in the future, simply because it might be requested within other blocks.
So. Hold tight. We’re getting there. And thanks for your support!