The changes for two pioneers of the digital advice space come as the sector matures; major banks and wirehouses are ramping up their own digital advice offerings, and a preference for hybrid robo advice has emerged.Betterment's co-founder Eli Broverman posted Monday on LinkedIn that he is stepping away from daily operations at the New York-based robo adviser. Separately, former Wealthfront CEO Adam Nash joined the board at micro-investing app Acorns, the firm announced on Tuesday.