If you offer services and you have a good feedback to other who have tries your services then you will surely get a monthly income.
It really depends on how good you do your job,if you are sloppy then you wont get any monthly income.
Otherwise it is not possible. But that also depends on the value that Bitcoin have and you never know that what it will be in the future.
Even if the price of bitcoin skyrockets we cannot afford to rely only on bitcoins, as we know that higher price is not permanent and it can fall back down in future.
but it is not difficult and hard that someone earn to live on bitcoin nowadays when there are a lot of different ways on internet to earn with bitcoin. If someone is intelligent he can earn in any situation with any opportunity.
People who have great skills will always find multiple ways for earnings, but the issue is what if bitcoin doesn't survive in future, they will have to divert thier work and earnings from other resources.