The idea for the Honda CRF450L was started by a few guys who love to do some Photoshopping, they even have a Facebook page (https://www.facebook.com/pages/Honda-CR ... ref=stream). But as they even say themselves “The models showed, doesn't exist. It's only a personal album, collecting my own ideas, how I think, that motorbikes should or could be.”
Honda has a 450cc single-cylinder trail bike available, the Honda CRF450X, sadly not available in Thailand. In Thailand only sells the not street legal Honda CRF450R for 310,000 THB. But even in the USA the Honda CRF450X (street legal) is not cheap as it's sold for US$ 8,440 (around 265,000 THB without adding transport cost, import duty and taxes).
But I agree that there's a market in Thailand for a 450 ~ 500cc single-cylinder off-road / supermotard style motorcycle, as long as the price is reasonable.