I'll pass.
" the second timelike coordinate is related to the (inertial) rest mass of a particle in both induced-matter and membrane theory."
The process of getting that mass and such processesthat are considered in QED cause me to think the d is spacelike, because x/c has always been used and observed as the limiting time. Lorentz invariance. I'd guess they'd never see Higg's particles in upcoming experiments if the d is timelike.
The Higgs field/boson, which has not yet been made or observed – is necessary to the Standard Model. If not found, another explanation is needed. But even if found, the Higgs only explains 5% of the critical density of the universe (ordinary matter). Hence, the search is on for supersymmetry.
Moreover, the 5D theories consistently propose that matter of all kinds in 4D is a manifestation of higher dimensional dynamics.
At any rate, the Higgs alone will not do the trick - nor even with superparticles do we have a complete explanation; therefore, the investigation continues for a geometric solution to understand mass. It's like peeling an onion, each layer tells us more.
For Lurkers, a recent Freeper discussion on The Mysteries of Mass
Concerning investigations into the possibility of violating Lorentz invariance, Lurkers might want to keep tabs on Kostelecky and Mewes. There's always someone picking at the paradigms in physics. That is one of the great things about the discipline, IMHO!