I agree this is a reasonable idea for one's long-term bond duration, but here are two caveats and one opportunity:
Caveats:1) Your money is locked up for a minimum term of ownership of one year, making I bonds unsuitable for emergency funds. If you sell before 5 years, you forfeit the previous 3 months of interest.
https://www.treasurydirect.gov/indiv/products/prod_ibonds_glance.htmYou might not miss those 3 months of coupons if the broader bond markets are right and the 5-year breakeven rate for inflation turns out to be 3.3%.
https://fred.stlouisfed.org/series/T5YIEThat prediction really raises eyebrows when you do the math and figure out how low the market must be expecting inflation to go to hit that 5y average after this period of 8.5% inflation. It would take one year of 8.5% followed by four years of 2% to average 3.3%, based on non-compounding napkin math.
2) Going long housing, long I bonds, and short a mortgage is a pro-inflationary trade. If in the next couple of years monetary velocity collapses and we get disinflation instead, your house could lose value at the same time as your I bonds stop providing any meaningful yield (and maybe at the same time rising unemployment makes it harder to earn a living). That may seem fanciful in light of today's headlines, but when one considers the effect rising interest rates are going to have on financial institutions' bond and mortgage holdings, not to mention their stock, crypto, and derivative holdings... a 2008-sized blowup by a financial institution somewhere seems quite possible.
Still, at least your I bond investment would return your principle in this scenario, which is more than we can say for most other asset classes. So if you're going to risk owning the house regardless, then the decision to invest in I bonds does not add more risk. The worst I can say is that maybe the 1 year lockup or the 5 year penalty could deter you from rebalancing as stocks fall.
Opportunity:There is a (perhaps temporary) hack married couples can use to lock in today's rates for next year's I bond allocation:
https://www.doctorofcredit.com/gifting-us-treasury-bonds-to-circumvent-10000-limit-i-bonds/