We do have a good sized "fusion" team focusing on product integration these days. Their mandate is to not only smooth out the integration process, but also to build some pretty kick-ass features on top of it. For example, between Bitbucket and JIRA these days you can not only view the code changes that relate to issues (and vice versa), but you can also transition issues through your workflow automatically based on the state of your commits, branches, & pull requests. We're also working on unifying the experience across the products. This started with the Atlassian Design Guidelines[1], but is continuing with product improvements like making the concept of a "project" consistent across Bitbucket Cloud, Bitbucket Server & JIRA (and making it easier to map them together). Integration and distributed systems are traditionally a tough problem in software, but we have some of our best engineers on it, so you can expect the cross-product experience to keep getting better!

[1]: https://design.atlassian.com/