Which code is open? You mean Bitcoin code, Not Blockstream's, right?
At this time there is no competition.
It is not likely that there will be any competition soon, if ever.
Adding SPV is really only for Blockstream.
Do you know the complexity of setting up a proof system for which these verifications are made? Look into it. It is a major effort taking some of the best minds many years and a LOT of computational power.
You are really arguing Blockstream will be the only one building sidechains on top of SPVproof !?
Blockstream has no code per say, they will write some for clients but SPVproof code is open source.
What's to stop Vitalik and the gang or Peter Todd and the crew from creating Blockstream2-3 when they realise that Blockstream business model is viable and is in fact the future of Bitcoin development.