http://gamespace.daemon-tools.cc/eng/news/the-players-have-no-rights-to-create-mods-in-gta-v-on-pc-2015-05-05
That's a link to the article
http://www.rockstargames.com/eula
That's a link to the EULA, where in the 3rd paragraph it says:
"You agree not to: reverse engineer, decompile, disassemble, display, perform, prepare derivative works based on, or otherwise modify the Software, in whole or in part"
If this is the case then this is a sad day.