I think we know by now that TM is not interested in the market outside Japan. Their laws limits them to under 1 Joule so why would they need to make their gear box support heavier springs?
Although TM have terrific detail and quality on their plastic injection and cast alum components, upgrading the spring for North American gaming will kill the TM gear box.
With more and more popular Polar Star HPA conversions, TM externals would be ideal.
Just recently Wolverine Airsoft announced their AEG HPA drop in kits with lower pricing than Polar Star, and it looks like they are undercuting Polar Star for a share of that pneumatic conversion business.
http://popularairsoft.com/news/wolve...-msrp-revealed