My suspicion is that HNO3 is more reliable because it is such a strong acid. Acid-base reactions occur extremely quickly, and can generate a significant amount of heat that is likely able to facilitate ignition of hypergolic mixtures.

HTP is extremely reactive, and more easily decomposed than HNO3, but lacks the strong acidity. Most metal-containing ILs I am familiar with have metals that are completely coordinatively saturated, but one could imagine either using a component of the IL that is an unsaturated coordination compound of a transition metal like Fe, Mn, or Co (all of which catalyze the decomposition of hydrogen peroxide, either to O2 and water, or to HO•), or just dissolving a small concentration of one of these metal salts (perhaps as triflates) in the IL to serve as catalysts to help initiate ignition.

PLEASE NOTE: I do not have first-hand experience working with hypergolic mixtures.

Thank you Aaron very much! Exactly, I have already tried the compounds that were promising with 98%+ HTP, but during the tests were quite inert because, as you said, the metal was completely coordinatively saturated! (this was not only in the case of ILs, I also checked some compounds with Co and MN - e.g. MMT, but without success...). And I have been thinking of "traditional" promoting ILs with some soluble salts in them... The problem, I guess, might be the solubility (e.g. in the case of DMAZ it was very hard to find a suitable, soluble compound that would act as a kind of promoting agent...)...

Have you tried acetylacetonates, especially Mn(III) and Co? If you have dicyanamide as anion, naturally, all metals are strongly coordinated, but the coordination with acac should be better. Other diketonates can be even better, like pivaloylacetone or tenoylacetone may be even better, as they are better soluble. 

Thanks Andrei! No, I haven't tested such compounds so far. But this is sth I'll look up soon...

I have seen also that for some reason iodine or iodide as counterion promote it with H2O2, you can try as well. Look here, for example, compare the ignition delay of the anions:

www.mdpi.com/2076-3417/5/4/1547/pdf

Thank you very much again - very interesting paper! I haven't seen it so far...

I believe there are enough literature examples of normal hypergolic ILs with nirtogen rich cations, so I wonder why you keep using metal cations?

as I expect them to have the lowest possible IDT with 98%+ HTP... Yes, there are quite a few in the literature that are hypergolic with highest grade of HP, but usually their IDT is rather low...