Running the Indexer requires a good amount of technical resources, including high bandwidth servers, databases, and other tech stack services (e.g. pagerduty, bugsnag, and more). We can expected the costs for running an Indexer to be significant (e.g. $50k or more). At the moment, there is no incentive for running an Indexer, it's strictly a public good that the protocol is dependent on. As such, the community should expect to fund professional teams and service providers that will run the Indexer on their behalf to support dYdX.
To improve the testnet experience, and to help the community scope out the role of the Indexer, the grants program is running a trial period of three months to run a live Indexer. Imperator have tremendous experience in the space, with expertise in data and APIs across other Cosmos protocols.