RSUs will typically all vest after a certain period of time, depending on the company (4-5 years?). But your mortgage is for 30 years. I wouldn't count that stock towards your "yearly income".
they vest over a period of time, not usually all at once. my company does it evenly over 4 years with a 1 year cliff. other companies can have it skewed towards the latter 4 years. employees do get refreshers as well. so if it vests equally over a certain amount of years, totally should count that portion towards yearly income. In your analogy, it's like counting how much you owe in mortgage payments every year towards yearly expenses.
RSUs refresh, or employees go to another employer for new RSUs.