I had a similar thought, but aired it too close to release. The technical side of things is that our API response only gives a limited set of results as you filter, so it has no knowledge of the maximum value that is available. We can attempt to let the user enter a blind value, but that could make for some very interesting error cases.
For example: Say I am narrowing down capacitors by capacitance. I keep dragging the slider further and further down so that I am only searching for caps that are 1 pF to 5 pF. Now I decide I want to widen the range and I type in 10, thinking it is in pF. But in reality, I might be typing in 10F, of which there are no results. This seems like an innocuous error, and it might be, but I think the concern was we wanted to constrain to the existing results.
Long story short, I like the idea and I want a similar feature, but we need to test it first.