Based on the latest ruling, Icathian Rain no longer creates 6 reflexive triggers, so what happen now if there is only 1 enemy unit with Deflect 1 on the board, and I have casted the Icathain Rain, but refuse to pay 6 extra power as the deflect cost? Does the spell still go onto the chain?

That premise isn't correct — under the current rules Icathian Rain still creates six separate damage instances (reflexive triggers), each with its own target choice. The card errata changed the wording from "Do this 6 times" to six "Deal 2 to a unit." lines, but the current official FAQ still treats it as six triggers that finalize one at a time.

Yes, the spell goes on the chain normally. Icathian Rain doesn't target when cast, so Deflect never demands 6 power up front — you cast it, pay its printed cost, and it resolves regardless of Deflect.

When Rain resolves, six triggers are created. For each one you choose a target, and if that target has Deflect 1 you pay the 1-power cost or decline — a declined trigger never finalizes and is removed from the chain (Rule 404.2). So against a single enemy unit with Deflect 1 you only need to pay for the triggers you actually want: pay 1 power for one trigger to deal 2, and if that kills it you may decline the remaining five. If the unit survives and you decline the rest, it just takes the 2 damage. You're never forced to pay all 6. (Related FAQ #3813 covers this exact scenario.)