Keep the weight limit; eliminate the size limit. No concessions for electrics. Did we learn nothing from the rule change allowing 20cc 4-strokes, but only 10cc 2-strokes? Besides the great incentive for manufacturers to develop high performance 1.20 4-strokes.
If size and cost are a concern then that ship has already sailed. Current pattern designs are big and expensive, but pattern has moved in the same direction since the inception of the FAI F3A world championships in 1960: bigger and more expensive. Back in the '60s the engine displacement was increased from 7.5cc to 10cc (cost at least one manufacturer a bundle as he'd geared up production for a high performance .45) and designs got bigger as more horsepower was extracted from the 2 stroke 60. 60 sized pattern ships grew to 850"sq and 66-68" long with the release of the Hanno Special and YS .61AR. Along came the 4-stroke. Not too impressive at first, then YS released the 1.20AC and designs got bigger, like Dave Von Linsowe's USA Star which was considered HUGE at the time. Levelling the 2-stroke versus 4-stroke playing field; displacement restrictions for both were eliminated, but the 2m size restriction was added. The result of the 2m rule was that everything was designed to 'fill the box' which meant increased power was required. We're now looking at the YS 1.70, OS 200 and the OS 1.60FX as the optimum glow power plants. Electrics have made incredible progress and seem to be competitive at present, but will certainly get better. You can now spend $5-8,000 on a top-of-the-line pattern ship without radio. The nature of competition is to push the envelope as far as the rules will allow, regardless of cost. There's an old auto racing axiom: speed costs, how fast can you afford to go? Paraphrasing for pattern: accuracy costs, how precise can you afford to fly? The best pilots in the world are simply striving to find the best 'tools' to help them achieve victory. There is still no substitute for effective practice.
Personally, I wish the rule had simply been changed to allow a displacement increase to 15cc for any glow engine (back in the '80s).
Pattern is still, by far, the most intriguing SIG in R/C - at least for me

PS - I would love to hear Wolfgang Matt's thoughts about pattern as he is clearly the elder statesman of the sport having competed in every F3A WC since at least 1971!!