It is not really such a bad idea to exchange your bitcoin to ethereum but you need to always have a plan in case things do not go according to your plan, as you can see the demand in the market of cryptocurrencies is going down and that is why we saw such a huge crash just a few days ago, but if the price of bitcoin begins to crash even more I have no doubts that altcoins will follow the same pattern and I think they could fall even faster than bitcoin.

So you need to watch the markets very closely and at the first sign of trouble you should exchange your ethereum back to bitcoin, but if you are not confident that the market will recover quickly enough you could try to get fiat instead.