Eastern don't do low cost operations, it's unlikely that they'd be interested in operating from Manston unless certain guarantees were in place and there was a proven demand for their type of service, although Manchester is a possibility.
The only realistic operator to AMS is KLM or VLM, as has been suggested previously the majority of AMS passengers from UK regional airports are interlining onward and no other operator can afford to provide such a service.
I've no doubt that low cost to Dublin and probably Edinburgh/Glasgow would sell like hot cakes, it's purely a matter of attracting the likes of Flybe, possibly Ryanair and that's no easy task given their demands.
Now that Eurostar have pulled direct services to Brussels from the UK, a BRU service may work, but competition elsewhere may put the kybosh on that.
As with many routes elsewhere, when one starts up, others follow, hopefully that will be the case here.