Here is my concern in how this Seth Jarvis type of contract can play out.
Draistaitl wants a contract for 8 years 13M after this year. Team X decides they will do it, but wants to defer all but 1M salary a year. But rather than offering 8x13 , with 1M salary and 12M deferred signing bonus, (96M in year 9), they enter into an agreement with an investment company to put 12M at the start of every year with a guaranteed rate of return of say 4% for 9 years (may very well be some companies willing to do this, its just a backwards annuity really). They know that will be worth 132M in year 9, so the offer becomes 1M a year plus a 16.5M per year signing bonus (132/8), deferred to year 9. Leon gets an extra 4.5M a year to defer, but it costs the team nothing as they only pay the 12M signing bonus a year, not 16.%, and they have 12M in salary cap space available.
Now that is an extreme case, but rich teams can certainly look at that in a new light.