So the point is to avoid using a stock late-model hazard switch? That does the job just fine, using a single flasher and no relay, and doesn't require that the ignition switch be on (potentially burning up the points) in order for the 4-ways to work. It also blocks Term 30 power from feeding back to Term 15, a problem encountered on some cars in the `60s in which all you had to do to "hotwire" the ignition was to turn on the 4-ways and hold the t'signal lever down. All things considered, it's a pretty elegant little piece of design, hard to outdo.
Put the second set of contacts in your DPDT switch to good use and make them select the power supply to the flasher (ignition-switched for t'signals, unswitched for hazards) and you'll have
almost duplicated all of the features of the stock hazard switch...you still won't have the red blinky in the center of the knob when the hazards are on
I can't remember how many times that's reminded me to turn the hazards off before signalling left to re-enter traffic.
