My apologies. My use of the words "built up" for describing bicarbonates in the soil was contextually inappropriate. They do no "accumulate" in soil in the classic sense that one might attribute to the over-application of soluble chemical fertilizers, until a certain soil solution pH threshold is crossed. By that time, nutrient availability in the soil has been severely compromised, and it's very difficult to come back from. It's much, much easier to raise soil acidity than it is to lower it. This has more to do with the soil solid phase chemistry (CEC), the "reserve acidity" that it carries, how it interacts with the soil solution, and how the chemistry of the irrigation water factors into the whole mess. It's pretty complicated chemistry, which I will admit that I do not fully understand at this point in time.
Bicarbonates in irrigation water react directly with hydrogen ions (soil acidity) in the soil solution, the net result of that chemical reaction being the production of water, and CO2.
There's not bicarbonate to leach. It needs to be neutralized prior to being added to the soil.
Sometimes I'm not the best at explaining things clearly so that others are able to understand the points I try to convey. This might help...
Also, I see a lot of people making determinations relevant to variables on water reports like hardness and alkalinity as "calcium carbonate". A lot of times, the value that folks assign to these variables doesn't mean what they think it means. The attached PDF clears up a lot of the confusion related to accurately defining some of these variables. I would encourage all who are dealing with poor quality irrigation water, or considering getting their water tested, to read it.
You should get your water tested before going the RO route. If bicarbonates are the only problematic soluble ion in your irrigation water, they're easy enough to deal with.
I've found, through experimentation, that using straight up RO can lead to the same problems related to soil pH that one is trying to avoid by removing the bicarbonates in the first place. It really does depend upon how much acidity (pH) the water is carrying to begin with.