TwitVid.io has to sue, or they might as well change their service name.
If they adequately established a trademark in 'TwitVid' via use or registration before TwitVid.com began offering a similar service, they'd have some chance of success.
It might not be cost-effective, though -- it could take a long time, and any similar use by the TwitVid.com owners/operators before TwitVid.io started might foul their claim. Even if they win they might not be able to collect much money/damages... though perhaps they could be awarded the TwitVid.com domain name.
Ignoring this or fighting TwitVid.com only in the 'court' of public opinion could lose any trademark rights TwitVid.io has -- by failure to enforce against a notorious and substantial infringement.
If they adequately established a trademark in 'TwitVid' via use or registration before TwitVid.com began offering a similar service, they'd have some chance of success.
It might not be cost-effective, though -- it could take a long time, and any similar use by the TwitVid.com owners/operators before TwitVid.io started might foul their claim. Even if they win they might not be able to collect much money/damages... though perhaps they could be awarded the TwitVid.com domain name.
Ignoring this or fighting TwitVid.com only in the 'court' of public opinion could lose any trademark rights TwitVid.io has -- by failure to enforce against a notorious and substantial infringement.