I WOULD LOVE for this to be open sourced! I am a 2x paid member since 2015 (4 years as at the time of writing) and have been so mostly because I wanted the keyboard and extra backup features. I assumed a multiselect would be a part of it, but it's not. I check back every now and then, but since it hasn't been happening, it has led me to testing other options. 

Unfortunately, I always come back to TO but it is so perfect (barring a few quirks that annoy me), it's almost exactly the tool that I want. 

Multi-select is a must purely and simply because:

* when you are organising your tabs (something TO is a fantastic tool for), you are doing it from your tabs outliner popup, not from the chrome browser that contains your tabs, so multi selecting tabs in the actually tab containing window is not the best choice.

* you can't easily identify which TABS (plural) you want to select (this is why I specifically you use tab outliner, because you can't see the tab names and if you have enough tabs open, you can't even see the icon! So which tab do you select for the first one, and which one for the last one? It is too convoluted, you need to select the first one and make a mental notation, "about the 4th one after that bookmark!" and then bring up the last tab, make the same notation and hopefully get the click right. This method ONLY supports neighbouring tabs

* when I browse I am often researching a few different things and continually get sidetracked. So it's not uncommon for tabs to be: 3 on topic A, 4x topic B, 2 Topic C, 3 more on A, 6 on D, 2 on C and so on. Trying to organise a mess like that is painful. YEs, I know it would be easier if I did something better from the outset, but sometimes you don't even know you are going down a rabbit hole until you have been through and investigated 4 new trains of thoughts you want to follow up! Because you can't read the tab names in the main window, organising these in TO is by far the best way to go, and every now and then I forget and shift-click and open that tab in a new window! DOH! LOL

* (the reason I came here today), when it comes time to making a set of tabs under another tab (so you can move it as a group), the only way I have found that possible within TO is to go to the last tab, CTRL+right, Up, CTRL+right, Up, (rince and repeat) and then flatten when you get to the second to last node (ie keeping it under the top node). Now if you are trying to do that to TAB that AREN'T consecutive, then it's even more cumbersome with: CTRL(UP +UP +UP + RIGHT) then Down, down, down, down, down, CTRL( UP, Up, Up.... RIGHT), LEFT, +/- (close the tree there) + DOWNx Y presses, CTRL(UPx Y presses, right)... etc etc.... It's unwieldy. 

But if you could shift and ctrl click the tabs.... that would be sweetness!!! 

* click the first tab, shift click the last tab, ctlr click a few more tabs and drag them all to the correct destination. 

If he no longer wants to actively develop features wanted by the community, it would be a huge bonus to the community if he did open source it, and it would be an extra special bonus if he stayed on as lead developer and still have a final say in push/pulls!! But I'm sure there are dozens of users out there who would be able to contribute in some way, even if they can't code. Improve documentation (not a great need there), triage and track new issues, review/curate suggestions etc. I'm not an experienced coder, but I understand code and would be more than willing to help document the source files (typical jack of all trades and master of none, I understand what I read, but don't have the necessary skills to put it together),. but even I would want to try and help out where I could. 

so #1, I would love to see multi-select, but #2, I would especially love for the community to be able to contribute to this AWESOME plugin! I don't for a moment regret having paid for it. Yes, it frustrates me every now and then, but I LOVE TO!!!! :D