I would love to see source of that claim that Nintendo is losing momentum, that's definitely taken out of context.
Nintendo is releasing revision because Switch is loosing momentum but simple because they always had handheld revisions around 2 yeas after launch (and Switch is esantualy handheld hardware), and most likly to offer lower price point in order to have much bigger appealing on market among families, kids and casuals, because Switch still has only one higher price point for that market, especially when 3DS that actually covers that price point is dying.
You've misunderstood my post: I wasn't claiming Switch is definitely losing momentum, but rather the Wall Street Journal report states that's the reasoning behind this supposed hardware redesign. See this USGamer article for a clearer indication of what Wall Street Journal say in their original report, which is behind a paywall.
If you read my post properly, you'll see I pointed out that a hardware refresh was only a matter time. I speculate that if Switch has lost momentum, that's likely down to this year's software line-up more than it is any hardware issue. I point out that Nintendo's major 2019 titles are yet to launch, and, importantly, that I think we should wait until Nintendo's second quarter results later this month before stating whether or not the system has lost momentum.