Disney has said the service will have 4k HDR content “where applicable,” although I don’t think they’ve said anything yet about just when exactly I-VI will be available to stream, at all, at any resolution.
It would be a little weird if the new master ended up making its first appearance in the form of a stream. For one thing, Disney would be undercutting their own sales of a physical UHD release if they were to do that.