Gentlemen,
Been following this with some interest, and I like what I see. (Mmmm.. a 3lb Pain In The Asp!!) But if I may offer up a couple of comments...

Weight limit, personally I would keep the limit 'RFL friendly' I.E. 3lb / 1.36Kg. Reasons, both other weight classes (f/w & h/w) have been agreed between the RFL & FRA, and to have a class that is very popular in the states with a different weight limit would put us back to were we were a few years ago with the feathers.
Plus with a machine of only 3lb in weight is far easier to transport across the pond than a feather, so I wouldn't be susprised to see a little 'Trans-Atlantic exchange' happening in the future if this class were to take off over here, but only if the two sets of build rules are compatable.

Active weapon rule, This is a tough call, I can see the attraction of active weapons from an audience point of view, but bear in mind that given the level of brushless technology available just how distructive a well engineered 3lb spinner could be. It has been the case at many events in the US that a good proportion of machines are written-off by a good spinner. How many of you want to build a new machine for each event!!
The only way to defend against this type of 'uber spinner' is the 'uber brick' and believe me those fights can be really spectacular. But the only way to build the 'uber brick, is to forgo a weapon.
So, this is the problem with an active weapon rule, have one and risk someone producing a very distructive machine and causing a lot of unnessary damage (and expense) to other builders therefore possibly reducing the number of compeating machines available for future events. Or don't have one and risk the chance of 'boreing box syndrome' but the chance of having more machines survive in the long term.
For what it's worth, as a new class and to make it as accessable as possible to new builders, I would not impose an active weapons rule for now. If you wish to change this in the future once the class is established and popular then fine, but if you go this route take the UK builders along with you and try to do it in consultation with the RFL.