Bingo... that's the whole idea here. Small teams within larger companies and small companies can use Trello. When they grow up (or need to interact with the rest of the company) they use JIRA. In fact I would expect JIRA integrations that make it trivial to convert a Trello card to a JIRA task, probably with an option to automatically convert a checklist into subtasks.

This acquisition makes total sense; Trello and JIRA target mostly non-overlapping market segments and there are some easy low-hanging integration fruits to be picked. I'll also bet Trello becomes a deal-sweetener going forward. License JIRA and for +15% you also get Trello for your whole company.