Sumitomo should take Sony over and merge its display division with NEC, keeping Sony just as premium brand in that market. BTW had it already taken it over, it could have merged with NEC its PC division too, that would have allowed deep restructuring of it too without ditching it altogether, and keeping alive the Vaio brand, so there wouldn't have been a sudden drop in PC sales.
Also Mitsubishi, Sanwa and other keiretsus could attain effective mergers or synergies between their existing companies and Sony, but in general, Mitsui is the wrong keiretsu to belong to, if Sony still wants to compete with Samsung in any market.
Maybe Sumitomo, having already important joint-ventures with Mitsui, should just merge with it and take it over...