If you read between the lines, over his entire letter then I think you are misinterpreting him by saying he switched from the "low inflation, Japan-style 10-20 year bubble implosion" camp to the "a decade of out of control, above average inflation, starting in 3 years" fanclub.
He puts together a secular anti-inflationary theme of household debt being paid off, a generation of babyboomers increasing savings, reducing spending, shifting investments into "safe", income generating assets, historic levels of slack in labor and global production capacity, an entire Western world operating with way less leverage and capital. In his estimation, this is nothing that is taken care of within two or three short years. He explicitly says he sees the (household and corporate sector) deleveraging process playing out over a minimum of 5-10 years (in the US).
