Well, I always thought Data could -- Gene Rodenberry did when he created his Data precursor, Questor from The Questor Tapes
. If I created a Data spin-off, I would have him and Geordi becoming a 24th century Sherlock Holmes & Watson with a bit of CSI thrown in, owing to their science & engineering backgrounds. They solve the most vexing crimes in the Federation, and wherever else they're needed.
As for who could realistically carry his own series, the Titan idea is intriguing. My idea is Riker is captain of another starship, with Worf as his Number One, on border patrol. It would be a dangerous assignment, protecting the outskirts of Federation territory from brigands and other threats.