This was discussed somewhere else before, and there's also a similar request in 0001296. So here's just a quick summary of my thoughts on this topic, and why it won't happen very soon:

• This feature mostly exists in chip trackers, for one specific reason: Because it saves memory. These trackers are often used in scenarios where memory consumption is super important, so it's an easy way to reuse data.
• I see the merits of reusing single channels, but it should never be the default mode: Once your song consists of more than just a handful patterns, it becomes very difficult to keep track of which channel data has been used where, and so an innocent change made in one location may have drastic consequences all over the complete track without noticing it until much later.
• As outlined in 0001296, I think a solution similar to what Disorder Tracker 2 did might make more sense: In that tracker, you have a timeline view similar to a regular sequencer, and in this timeline view you can arrange patterns freely, including overlapping patterns. That way, you can work with "normal-sized" patterns by default but if you wish to reuse just a few channels in some places, you can do so by creating a smaller pattern just containing those channels and then combining this with the normal-sized patterns. That way, the default tracker workflow is preserved while also allowing a similar workflow as found in chip trackers.