It would be nice to build in cash flow modeling leading up to and through retirement with earnings and withdrawals optimized for minimizing taxes. something like PralanaGold
Tiller is not going in this direction. To do it right, people definitely need a tool like you mention.
I use the following:
NewRetirement just added account linking of balances via Plaid. Transactions are next.
Monte Carlo is coming soon. They have great retirement distribution analysis. They have free and paid versions. The product looks at planning over a lifetime which is what you need. Great tax analysis. The charts are impressive. They have the best Roth conversions analysis that I have seen. They are serious about feedback. I have had numerous calls with the owner, design teams, etc. No, I do not have an ownership interest. Give it a try. You have nothing to lose. Let me know.