Not that much I think. But lets first define what DIY smarthome really is...
- Does it mean those that build their own system from scratch (like you did?)?
- Or does it also include those that contribute to an OS smarthome project to add the things they are missing?
- And what about those that buy a commercial product and tailor the product to their needs as much as they can? (e.g. defining their own events/scenarios/rules)?
(You'll find all of those here on this forum BTW

)
I think it's safe to say that the market becomes larger with each 'yes' to the 3 questions above, but it still remains small.
Cause the majority (those that like what they see when they're visiting "our" homes and ask where they can download the app) will always want something that works out of the box and in my opinion smarthome is not ready for that yet - you either pay an expensive bill or spend a lot of time on DIY, and I think it will take some time before this will change.