I don't know, hypergolic propellants are really nasty, toxic chemicals, as well as (I would imagine) being expensive to produce. I think that far outweighs the added complexity and mass of an ignition system.
There are many engines that use non hypergolic propellants, and they do just fine. There have even been proposals to replace the hypergolics on the shuttle with LOX and alchohol, and the GOX/Sintin system obviously worked for Buran (which my system is inspired by).
Hypergolics are tried and trusted, they're very familiar, but I look at this spacecraft, with it's futuristic propulsion system, and I figure, that a little greener secondary propellant couldn't hurt.
Nevertheless, I am unsure of my propellants as I have them now, and I have other concepts as well:
GOX/CH4: Advantageous because fuel is shared with main propellant. Crossfeeding on-orbit would probably be impractical, but it could simplify ground handling. Advantageous because gaseous methane removes the need for secondary pressurant for the fuel, but gaseous methane will be less dense than sintin.
H2O2/Hydrocarbon: A mixture of hydrocarbons (ethylene/propane, etc) is self pressurising, and pressurises liquid high concentration H2O2 via means of a collapsable membrane (as per
this study). No secondary pressurant is required, and with the inclusion of a catalyst, hydrocarbon/H2O2 is hypergolic (Bristol Siddely Gamma is an example of this sort of system). H2O2 does not have the toxicity of hypergolic propellants, but it is a very strong oxidiser and could prove to be unstable.
H2O2/Sintin: Similar to current option, but with GOX replaced with H2O2. Both propellants would need to be pressurised by secondary gas sources, although peroxide decomposition removes the need for an ignition system.