See Who owns the network? rather than re-hashing here. But a very short summary
i) It may be against T&C's of ISP to overlay TTN/Gateway on top
ii) There's a real danger of a gateway/TTN being classified as a PECN under Comms Act, which means there are obligations that have to be abided by (even if just an ECN, still obligations)
iii) With IP Act coming into law (and existing law such as RIP/DRIP/E-Commerce Act) there may be requirements. Being a Communications Provider (which TTN pretty much is) could have legal implications.
iv) All kit sold must be CE marked (or distributed/given away at courses).
v) R&D use (without a non-operational license of some sort) is limited to 30m between devices if not CE marked.
vi) The Wireless Telegraphy Act is extremely punitive (historic reasons), but breaking it can mean prison and/or heavy fines.
Most people here would rather just do something and not worry about the regulatory aspects or just cover the ears and ignore them.
[Moderator note: please respond to anything of the above in the existing topic. Thanks.]