I think:

1. Introducing a general max. take off weight of 5.4 kg would make it possible to enter with a reduced cost, because:
A. You could possibly use a gas engine.
B. You could use an old damaged/repaired model that would otherwise be overweight. (Glow or electric)
C. You could use cheaper batteries, such as 5000 mAh packs from HobbyCity instead of 4350 or 5000 mAh packs from ThunderPower, and cheaper motor/regulator.
D. Making a composite airframe at 3 kg. rather than 2-2.5 kg. is cheaper. (I make my own composite models, and reducing weight is expensive and time consuming.)

This weight increase would therefore be good for those that want to enter at a low price/budget, and therefore POSSIBLY increase the number of entrants.

2. It would make it more expensive to be truly competitive, because:
A. YS can now develop a 2.0 or a 2.2 that has 30% more power, (CDI of course) and still be ok for weight.
B. The competitive electric pilot would still use a light (expensive) airframe and take advantage of the weight increase to increase power by carrying larger battery packs, bigger motor etc.

From my point of view it therefore boils down to what you want to achieve, and which end of the scale you are prioritizing.

Reduced min. cost, Yes.
Increased max. cost: Yes.

Magne (In Norway and therefore not AMA affiliated, but the principle of this discussion is universally applicable. Most countries have entry level classes.)