Was looking over estate plans.
Current directive is liquidate everything (including Berkshire!) and put 90% in RSP and 10% in cash equivalents.

Thoughts?

This would be instructions for when you are gone and/or unable to manage investments? Instructions for whoever is managing the estate investments but has no skill or ability or desire to do active management?

Then:
50% VASGX (Vanguard LifeStrategy Growth Fund) (80/20 fund)
50% VTSAX or VTI ((Vanguard Total Stock Market Index Fund)
Additionally: "When you withdraw money, take it from whichever fund has the highest value". (This moves the portfolio back toward 50/50. But they don't need to understand that, they just need to do that.)

That's a 90/10 asset allocation.

You need "explain it to a young child ... or a golden retriever" level of instructions.
You want something that that an unknowing person can easily justify and that can't really be questioned. I think that RSP & "cash equivalents" are not that.

Those Vanguard funds are well known and well diversified. Nobody can argue that they won't be around forever, or they are too risky, or need to have the mathematical advantages of "equal weight" explained to them.