The airports press release seems to confirm that Eastern are basing an E190 at Southampton. Hopefully they'll be able to recruit some ex.Flybe Embraer crew locally for it.
“This is also a new destination for the airport and a positive step forward given the challenging conditions our entire industry continues to face. We look forward to working with Eastern to develop this service further and welcoming the first passengers later this year and indeed the basing of an Eastern Airways’ Embraer 190 aircraft to make this route and others possible.”
I wonder where else they'll look at? Alicante seems like the most obvious omission, along with Verona (popular with tour operators and attracted some rather high fares). Beyond that maybe some of the longer French routes - Avignon, Perpignan, Toulon, Bastia. Further out the box would be trying a new unserved market - Croatia has grown significantly in popularity since Flybe served Split and Dubrovnik from Southampton about 10 years ago, as an example.