I don't really see big opportunity costs for Bitcoin hodlers if they provide liquidity for Lightning,
Agree, as it's actually a virtuous circle: the more participants/services join, the lesser the opportunistic cost. The lesser the opportunistic cost, the more new people join.
Not even mentioning protocol upgrades that help this move forward (eg splicing out).
So it's not really different if you hold the BTC (improductively) in your wallet.
Strongly disagree ! You are leaving your coins in a hot wallet on alpha software (and protocol!) here.
So it *is* different, just a trade-off (that a lot of us choose to make, at least for part of their funds).