If you're not actually getting anything semantically useful out of the element, then you may as well use a custom element.

Also by using a custom element instead of a class, you're saying this isn't anything else other than what I say it is.

It's not a <section class="swim-lanes">, it's not a <form class="swim-lanes">, it's not a <blockquote class="swim-lanes">, it's a <swim-lanes>.

If you make something only a class, people end up misusing it in odd places.