In finance, we have the concept of
* short- (less than a year),
* medium- (1 to 5 years),
* long-term (5+ years) savings,
* and reserve (no plans for spending).
Discussion
The reason why Bitcoin even beats gold as a reserve is because you can keep information about it to yourself (so that you feel confident taking on a loan, for instance), you can store and transport it yourself, and you can publicize its existence by merely proving ownership of a particular key (so that someone else is reassured of your solvency).
That is why the ability to spend Bitcoin easily is not required to make Bitcoin the best reserve currency. Ease-of-spending is not a requirement of a money you never plan on spending.
And, if you are already using something for your reserve, it makes sense to build at least one of your savings vehincles from the same base, for simplicity's sake and to maintain the primacy of your reserve asset by promoting its velocity.