You can keep the bars, but you don't list market share percentages anymore. That way you won't have to put Switch twice on the frontpage.
I know it's unfortunate, but there is not a simple solution when the number of platforms has been reduced from five to three. Nintendo combined their home console and handheld while Sony exited the handheld market. It's a small section of the frontpage, so I cannot imagine that it would be a lot of work to implement a new design. Convincing Brett to get it done is the hard part.
StarDoor had a good idea when he put release years under the bars for console sales. I can also get behind the idea of using market share percentages for year to date sales that include consoles from two different generations.
Change is always going to be controversial and you are never going to please everyone. But it's a fact that change happened and you won't get around the new circumstances in the video game console market. You have to figure out what makes the most sense going forward. What are you going to do when the PS5 launches? If you keep market share percentages and then swap the PS5 for the PS4 on the frontpage, Sony's market share would drop from ~60% to under 5%. Removing market share percentages is going to be a lesser evil than retaining them.
Regarding your question. Assume PS5 releases in, say, 3 years' time, and the Switch is continuing to prove a great success, so Nintendo has no plans for a new platform anytime soon. In that situation I'd say the home console chart would be just Switch and PS5, with XOne being dropped entirely. The next Xbox console would then be added to the chart when it released.
Sure this'd mean PS5 having almost no market share at first, and Switch having 90+%, but that's jsut the state of the market at the time and no different from the Xbox 360 headstart during that generation.
Like you say it means making a call and no one will be entirely satisfied. But if I were to make that call right now it would be:
With market shares and with date of release, and with the chart being renamed current platforms. The handheld chart would be removed once both Vita and 3DS stop being produced. If Nintendo releases a new handheld then it would have 100% market share. If they don't, then handheld gets taken down altogether. Switch fits more comfortably in the console section than the handheld one imo.