So, why do we want to become an Eclipse project even though mbeddr is not based on Eclipse technologies (but instead on JetBrains MPS)? The main reason is that we can apply the Eclipse governance process to mbeddr. This is very useful for companies who want to use mbeddr for real world applications. Two advantages are particularly important. The first one is the IP review (which we still have to complete), which indicates to prospective users that the code does not infringe on patents. Second, Eclipse defines a process how new people can become committers and hence contribute to, and influence the direction of mbeddr.
Another reason for joining Eclipse is that it's a nice community, in which many of the mbeddr team members have been active for a long time. We are looking forward to it :-)