The titanium barrel blank would probably be profiled while lathe centered on the steel liner. It would have to be done by a competent machinist, though, taking into account Ti's prospensity to 'give' against the cutting tool (from what I hear). If machined improperly it would be out of shape, thicker in some areas and thinner in others, because the material slipped under the tool instead of digging in.
As for thermal expansion coefficient, steel expands more than titanium. Get it hot and the liner would simply fit tighter in the Ti barrel. Ti has elasticity and would probably stretch with the liner as it expanded, with no ill effects (emphasis on 'probably'). Of cousre get it hot enough, fast enough, and there might be deformation or even splitting (I think this is extreme, though).
Titanium's thermal conductivity is slightly better than steel.
Ti has a Young's Modulus around half that of steel (and a bit higher than Al), so it's not as stiff.
I am no metallurgist though, nor am I a barrel maker, so take it for what it's worth (about US $0.01).