It might not be the best but i think it would be nice for someone to invent a weather radar that can plug into the nav unit so you can watch the weather if need be.. again not the best idea but would help some people
Be patient. XM announced at CES early this year that they will expand their WxWorx service to include aftermarket weather receivers/tuners for their satellite radio service. Don't know if Pioneer will actually build an AVIC-compatible one, but XM will be offering the weather service to individuals real soon. If I can find the press release I will post it here.
Actually it was CES 2006 
Now I am not too sure since that was 18 months ago
Wow NOAH style info. That is cool and would be nice but the price is kind of high. Am I reading this correct? $100 for setup then $100 each month, then it is $7 more for radio. That is over $1200 a year for weather maps! 
I would think a few different packages would be a good idea. Less $ each month for less weather maps and info.
http://www.xmradio.com/pdf/existing/weather/grd_subscription_pkg.pdf
I have xmwx on a Garmin 376C and it rocks. The prices are misleading as they try to upsell the most expensive services- the "mariner" package for fisherman has a lot of good info and is a lot cheaper per month. The hardware to run XM wx on laptops etc for weather chasers is still big money- a solution that would work with existing popular NAV units is a no-brainer, but isn't as simple as just an RCA input kinda thing because it has to overlay over the NAV screen.