I love your idea and it's one that I've had for a while.

Currently, the market for bitcoin developers may be small, but it will only keep growing in the future. As you said, the market may be small because there are high barriers to entry, e.g. there is demand but developers are waiting for an easy and simple way to configure and deploy their bitcoin app. Abstracting bitcoind calls with a REST API could be one way to go. You could have bits of code for the most popular web and mobile frameworks that developers add to their app to bring up and connect to an instance of bitcoind.

Obviously the big question here is security, but if you provide enough value to developers and military-grade security, they will come to trust you. Coinbase has 300K users, and all their bitcoins are stored on servers customers don't own.

It's a big undertaking, but I can tell you there's definitely (gonna be) a market for this, as long as you focus on great service and security.