I'm surprised that all of the new and improved tail light PCBs haven't been made with layouts that would facilitate plug & play sequencers.
Like, integrating the pads for a sequencing connector and creating an easy to sever copper bridge.
"Want to add our sequencer kit? Simply cut these bridge traces with a knife and plug our module into the second, unused edge connector."
Or you build a new PCB with each lamp wired discreetly and featuring a weather resistant terminal.
Then you offer a stock plug & play adapter for a drop-in upgrade
...or a weatherpack cut & crimp terminal to get rid of the card edge connector
...or an add-on adapter for a sequencing module
Please make checks out to "Mr Bombjoy, c/o Million Dollar Idea Club"