The first link you provided says it applies "for projects that begin construction after 2020 and before 2027." So I'm not sure if it would be retroactive to 2020, or if "after 2020" means 2021. If it were to be retroactive to 2020, and assuming it is not implemented before we file our taxes, those of us with 2020 installs would likely need to file some sort of amended return to get that extra 4%. To be honest, even though it would be a bonus for me, making it retroactive to 2020 would be stupid since customers agreed to their purchases under known pricing/credit conditions (but, as I mention above, there is precedent for this stupidity in how they extended the energy efficiency credit.) To be clear, Congress could pick any day they want - it does not even have to be the beginning of the year - though for ease of implementation, it seems like they generally align it with one.
For the PWs, I am almost certain it would not be an additional 30%. All it would likely do is codify that PWs do, in fact, qualify for the ITC, where right now, the law is silent on the point and we are all relying on an unofficial IRS interpretation. So, it would help provide some certainty for PWs and, depending on the exact wording, potentially expand the allowed use of a qualifying PW, but it would still be a single 30% credit under the revised ITC.