Bitcoin is there to stay because it provided several new services before the others did. All these other blockchains, might they be developped by Ethereum, Microsoft or Linux, will all cover different fields of use. Ethereum is there to deal with computer programmer's stuff, to record services brought by programmers, it's all very abstract. Also this blockchain that Microsoft wants to develop will be used to track stocks, bonds or houses. None of them is a threat to bitcoin because both of them operate on different fields of use. Bitcoin operates in the field of currencies, Microsoft in the fields of stocks and Ethereum in the field of computer services. All three can coexist without problems.
Linux wants to develop a blockchain together with JP Morgan, now, and that one is the only one that is aimed directly in the same field as bitcoin's (i.e. currencies). It's the only one going head on with bitcoin. But seriously who wants a blockchain currency backed by banks? It's plain stupid. The winner of this war was decided before the war even broke out. It's bitcoin, definitely. A bank-backed blockchain can still co-exist with bitcoin's, now, don't make me say what I didn't say, but it will remain much smaller, and thus will never be a threat to bitcoin. Actually it might even help it get bigger by bringing more people to know about the blockchain and cryptos.