Update
What I see in the OP message is "well, I don't really know what we need (thus the lack of detailed requirements), but may be some enterprizey tool will magically solve all our problems, known and unforeseen? That would be awesome!"
With an architectural approach like this it's not gonna fly. No success stories from Teracotta would change that.
OSS is beneficial when the community around it can replace the commercial support. Suppose the guy have a problem in production. Community cannot help -- it's too small for the obscure product like this. Servers are down, business is in danger. You see? You need a commercial license up-front. No money? Well, then you're not a business, and probably not gonna become one (if nobody's willing to invest into it).
Sorry for interrupting your day-dreaming.
IMHO:
Terracotta is a clustering solution. Clustering is required for large, enterprise-grade applications. Large applications mean big budgets. Big budgets mean you can afford commercial license from Terracotta.
To put it in another way: if you don't have budget to buy it, it's probably not beneficial for your project.