Eclipse 4.14 (= 2019.12) added support to show problem markers inline. There’s a screenshot in the “New & Noteworthy” at https://www.eclipse.org/eclipse/news/4.14/platform.php#show-markers-as-code-minings .
The feature is still quite new and there are a few issues to be worked out (e.g. behaviour when code is still being edited, see https://bugs.eclipse.org/bugs/show_bug.cgi?id=553849 ).
Would it be possible to add support for inline markers for the markers added by SonarLint?