With densely packed decimals (3 digits in 10 bits), you can reduce the space overhead to as little as 2.4% (1024/1000). The IEEE has even standardized various base-10 floating-point formats (e.g. decimal64). I'd suspect that with dedicated hardware, you could bring down the compute difference to 2-3x binary FP.

However I read the post I responded to as decrying all floating-point formats, regardless of base. That leaves only fixed-point (fancy integers) and rationals. To represent numbers with the same range as double precision, you'd need about 2048 bits for either alternative. And rational arithmetic is really slow due to heavy reliance on the GCD operation.