I'm not sure if English laws allows substitution, but technically in US law this contract indeed don't have a consideration. While mutual consideration makes it enforceable, the lack of it doesn't automatically make the contract void. You could argue that there's promissory estoppel:

> Promissory estoppel/detrimental reliance: A contract without consideration is enforceable if the nonperformance of the promisor will cause injustice. Elements of promissory estoppel are (i) the promise has reasonable, foreseeable, and detrimental reliance on the promisor, and (ii) the enforcement of the promise is necessary to avoid injustice.

In this case, you are nearly correct that the performance to honor the terms of the contract is essential, but technically not a consideration. (The IP code is consideration though.)

The software project gives the other party IP to use, and gets nothing in return. Might not even be told the other party is using their software.

I don't think accepting a contract can qualify as consideration for that contract, as otherwise there would never be a need for consideration in any contract.