A currency which decays over time is definitely not a store of value. But the way I see it, it’s only use case, the security would be provided by the programmatically inalterable feature of self-replenishment each month.
Basically, it would work almost as a “voucher” system. In dire economic crisis, States have sometimes issued “single lunch vouchers” to the population which were redeemable against a meal given by public services, so as to ensure that at minimum, people had enough to eat.
This self-replenishing and decaying crypto-currency would serve precisely that purpose only: provide access, on a monthly basis, to enough “virtual vouchers” to purchase anything, but especially meet the most essential needs.
This is what Universal Basic Income seeks to cover anyways, hence the use of the word “Basic”. It’s aim is not to allow people to save, put money aside, it’s only to ensure people are not coerced into taking up any job at any condition in the labour market because they would otherwise not have access to food or shelter.
The fact that the currency self-destructs is specifically to encourage consumption, that is, that people use it to cater to their most basic need and use any other regular currency (official fiat, or your proposal) for the purposes of savings and long term planning.
On a global scale, imagine the following: a myriad of regions each with their own unique basic, self-replenishing and decaying crypto-currency, allowing the people living there to purchase products and services of first necessity. Any surplus produced would either be consumed locally with traditional fiat currencies or would be open for trade. By giving people “virtual vouchers” with a time limit on their use, you make sure that what has been produced locally is consumed locally first, before being shipped abroad, forcing diversification of production, something that is more and more possible by the way with technologies allowing economies of scale without the need for concentration (for instance, 3D printing technology which allows for producing just about anything without the necessity to build a single purpose mega-factory).
To finish, it wouldn’t really be “forced consumption” since the value paid each month of such a crypto-currency would be calculated based on the most basic physiological human needs, so this would be consumption that would have happened anyways, with or without the decaying feature (they are called irreductible expenditures I think, including food, shelter, water, electricity…). The decaying feature is there simply because of the self-replenishing feature. It is as if each month, you would redistribute all the money exchanged so that each person starts again with the same amount. But it’s simpler to make it self-replenishing and decaying programmatically, since it works in a familiar way to all people: at the end of the month, you get your “monthly pay check”.
