I agree we need to promote pattern and devise ways of growing it, but I don't think a weight limit change will do that. I feel it would only increase the costs needed for those currently competing and I feel that we would lose as many current fliers as we would gain in new ones.
The process at the worlds is as follows,
- All aircraft are processed prior to the competition, this checks weight, size, identification, RF transmittal, as well they sometimes check the receiver to see if you have a gyro plugged in.
- After each flight your plane is quarantined and weighed (and re-noise tested at the first available opportunity if applicable). Glow guys can remove fuel only for the weigh in, but I don't think they are allowed to clean the model, so you can't be too close or the oil might get you

Electric are not allowed to do anything to their planes and are weighed as flown. If you passed the processing weigh in but fail a flight weigh in, they can assess a penalty to your score, I am not sure how this is calculated.
I have only seen once where someone failed the post flight weigh in, it was a glow flier and was given a 3% penalty I think, this was at the worlds in France. Under the new rules with the allowance, he would have passed that check.....which is why they are there now