Just wanted to take a quick look at this timeline:
Nintendo 3DS came out February 2011.
Between Feb 2011 to Dec 2012 (22 months), no kernel exploits discovered. Firmwares 1.0 to 4.0 don't yield anything interesting.
December 2012, Neimod discovers a big one, but brags about it. Tech news sites, blogs, and forums fill with speculation and chatter. It quickly catches Nintendo's attention.
Neimod, realizing the jig is up, quietly sells exploit info to a Chinese team (allegedly), who end up making the Gateway.
Before Gateway is even announced, Nintendo already found the exploit and patched it in less than 3 months with update 5.0 (March 2013).
August 2013, first flash cart comes out with Gateway promising "support for 6.x+ soon", which we know is not possible.
Another note:
Firmware 4.1 came out in May 2012, and the exploit was discovered in late December 2012. It took over 7 months for it to be found (assuming Neimod was searching since May 2012).
Nintendo are going to be meticulous with future updates, not risking another exploit "slipping through" like they did in the 4.1 update. So the chances of a kernel exploit for 5.0 and above anytime soon is very slim.
I don't understand the logic behind people here who say "I'll just wait for an exploit for my 6.1 3DS". It's not going to happen.