I'm not sure your proposed solution will work unless we assume people exclusively send signal X or Y. Whoever is subsidizing people to send signal Y needs to have some relatively simple process of identifying the people they want to subsidize to send signal Y. In the MIT degree example you gave the process was simply selecting people who were already sending signal X, but you could also try to identify individuals who have an obviously high Z.
Since the subsidizer can identify people who should be subsidized, then so can I as an employer. If you come to me with signal Y, then I will check whether you are likely to have been subsidized to send signal Y rather than signal X. If you were likely to have been subsidized, then I will accept you since you had a good incentive to choose Y over X. If you are unlikely to have been subsidized, then I will assume you chose to send signal Y because you were unable to send signal X. What is going to become culturally acceptable is sending signal Y in conjunction with a signal that you were incentivized to choose Y over X. Sending signal Y by itself will continue to be seen as a fallback for those who couldn't send X. Effectively signal Y will be split into two separate signals:
Signal Y+ = Signal Y and proof that you had an incentive to send Y over X.
Signal Y- = Signal Y, but no argument for why you chose Y over X.
Your subsidy will only increase people sending Y+, employers will continue to see Y- as proof you couldn't do X or Y+. And the moment you stop subsidies no one will have a reason to send signal Y+.
If you could somehow make Y+ and Y- hard to distinguish, then it could work but I can't come up with a mechanism for accomplishing that.
I'm not sure your proposed solution will work unless we assume people exclusively send signal X or Y. Whoever is subsidizing people to send signal Y needs to have some relatively simple process of identifying the people they want to subsidize to send signal Y. In the MIT degree example you gave the process was simply selecting people who were already sending signal X, but you could also try to identify individuals who have an obviously high Z.
Since the subsidizer can identify people who should be subsidized, then so can I as an employer. If you come to me with signal Y, then I will check whether you are likely to have been subsidized to send signal Y rather than signal X. If you were likely to have been subsidized, then I will accept you since you had a good incentive to choose Y over X. If you are unlikely to have been subsidized, then I will assume you chose to send signal Y because you were unable to send signal X. What is going to become culturally acceptable is sending signal Y in conjunction with a signal that you were incentivized to choose Y over X. Sending signal Y by itself will continue to be seen as a fallback for those who couldn't send X. Effectively signal Y will be split into two separate signals:
Your subsidy will only increase people sending Y+, employers will continue to see Y- as proof you couldn't do X or Y+. And the moment you stop subsidies no one will have a reason to send signal Y+.
If you could somehow make Y+ and Y- hard to distinguish, then it could work but I can't come up with a mechanism for accomplishing that.