I propose another possibility, inspired by the original meaning of a bond coupon. From Coupon Definition
Coupon Bonds
The term “coupon” originally refers to actual detachable coupons affixed to bond certificates. Bonds with coupons, known as coupon bonds or bearer bonds, are not registered, meaning that possession of them constitutes ownership. To collect an interest payment, the investor has to present the physical coupon.
The idea
Create an ASA corresponding to each payment deadline, and the the final principal. When you buy a “bond”, you get one of each. When you wish to get paid for a coupon, you send it to a smart contract that pays you out (assuming the deadline associated with the coupon has passed). Same for the principal.
Now the coupons are individually tradable which seems like an advantage. And the “tracking” is only on the number of payment deadlines, rather than number of bonds issued.