People who are comfortable with paper money will only use paper money even if bitcoin hits the mainstream as they will find easy way to spend their money, and paper money will take care of it.
These are some people who do not want to accept the change. They cant digest change from paper currency to Digital. If it is possible we have to educate them so that they get to know the benefits of this Bitcoin currency and hence they start using it.
I believe change is already happening either we like it or not lol.
Money has been evolving in our generation form, like the whole square, apple pay, etc. Its only natural if we see bitcoin becoming the new form.