Yes, Game Boy Player technology is VERY simple (it's been around since the N64 days), and rather cheap to implement. Putting a small slot for regular and Advance carts right at the system's helm would be very effective. Then, dual layer the disk player so that GC disks can click right in and be read, and full-size DVDs can fit in and be used as well (not simulataneously, of course). Then, Nintendo should bill these features as huge selling points for the system. The GB, throughout all of its installments, has accumulated thousands and thousands of titles. The GC, by that point, will probably have a good three to four, maybe even five hundred games. Combined, this new system would have a huge library of great games right out of the gate, appealing to the HUGE handheld crowd with a home center to play all of their favorite portables on, and to gamers of other systems with its access to all of the older GC along with all of the new. And though MOST people will have a DVD player by then, people who value saving space and getting more for their money will find the inclusion of DVD playback very nice. And no regional lockout. For anything.
I think Nintendo should use full-size DVDs for their games, or else the competition will have an advantage over them with MUCH larger disk capacity. Seriously, having to spread Resident Evil over two GC disks when they both could have fit effortlessly on an X-Box disk with room to spare is pretty... pathetic. My personal favorite game, Eternal Darkness, also was victimized by limited disk space, sacrificing the quality of its otherwise awesome cinema scenes so that it could make it all onto one disk. Sure, it may be a foolproof against piracy, but I'm sure there's other ways around the problem without slicing so much into disk capacity. Nintendo needs to be a little more conservative with its action and meet the competition toe-to-toe.
Madden is important. I hang out with a lot of "jocks" (I really don't like that word, it's stereotypical), and to them Madden IS bread and butter. And, according to sales charts, it's the bread and butter of hundreds of millions of other gamers all across North America. No matter how "universally" popular Madden may be worldwide, delivering the top version of the game on Nintendo's next system and billing it as the best will help to establish a strong userbase for the console her in the states, something that pays off in the long run. Also, Madden is MUCH more plausible then GTA, and Nintendo already has good ties to EA.
Another place where Nintendo needs to put its money is at retail chains. Back when the consoles launched, it tore at my heart to go to the mall with some friends and see EB and FYE filled to the brim with X-Box advertisements, while a single GC kiosk, some obscure posters, and cardboard stand-up were tucked away in the back. Most of the people browsing through the stores there had no idea that not just one new system was coming out, but TWO. Nintendo's presence at the market was overshadowed by Microsoft's more aggressive stance on pushing the product into the lime light. With the next system, they need to change all of that. They need to gamble a bit and pay the big bucks to secure the advertising rights in major retail outlets, like Electronic Botique. They need to do what they did with Resident Evil's launch; they need to secure several months of Nintendo-heavy advertising, so that Nintendo game posters and cardboard cut-outs and memorbolia adorn the windows at the front of the store, so that several koisks are available for play, so that the bags are imprinted with the Nintendo logo, and so that the employees answer the phone saying, "Greetings from EB, where we are celebrating Nintendo week! How can I help you?" They did it around the time Resident Evil launched, but that wasn't nearly soon enough. They need to do it at LAUNCH. And they need to do it ten times greater. Nintendo needs to practically force their new system into the casual consumer's hands. Nothing else will do the trick.
Imagine coupling that EB advertising strategy with a launch that came a full year AHEAD of the competition. A huge, explosive, well-known launch, and then a full year to follow through with and build momentum, to build a head start. They need this. All it takes is a good single and multiplayer game packed full of Nintendo charm, a wide array of popular third-party titles, and the willingness to spend some money on increasing awareness. Put this all a year in advance, and you'll have units selling like crazy.