Even if you assume BTC stops increasing in value (something I don't think will happen until its price is far higher) its limited supply makes it deflationary rather than inflationary like, e.g., the US dollar (that's lost over 90% of its purchasing power since I was born).

This means any interest you get by lending it is at least on top of the US dollar inflation.

When inflation is, say, 3%, if you earn a 3% interest rate on BTC it would be 6.09% interest in dollar terms.