I think the reason we're hearing more about the Swedish ISK comes back to the severe conservatism within the Department of Finance.
An ISK system would be potentially more complex for an end user than an ISA, eroding the benefit of "simple product, wide take up."
But, crucially, an ISK system passes significant risk from the state to the individual end user. It's a predictable government tax on assets - in a good year where the value of assets under management over a tax free allowance rise by 10%, the government revenue will rise by 0.1%, but in a bad year where the value of AUM fall by -10%, the government revenue will fall by -0.1% (very roughly speaking). This is a €10m swing for every €10bn under management (over the TFA). Probably a bigger swing in a bad year as more comes under the TFA, but a bigger upside in years where amounts go over the TFA, depending on investor behaviour.
The DoF has shown itself to prefer getting its end over most other considerations time and again, and shown themselves to be instinctively anti-wealth creation where there is any risk to the tax base they can see, and so be it to the foregone potential economic benefits.
Look at the operation of things like the KEEP scheme (and most other share option schemes for employees of non-listed firms). Look at deemed disposal. Look at the SFT for pensions not rising with inflation, until senior public sector workers started to run into it recently. Look at the tax free allowance for CGT sitting at the euro-translated £1,000 of €1,270 for decades.
Never mind that share based incentives to employees helps drive a dynamic domestic start up scheme (and the treatment of employee share options in publicly listed, typically multinational, players is a lot friendlier). Never mind the unfairness that the SFT has been eroded by inflation significantly to date for private sector workers. Never mind that we have billions sitting on ice in deposits we want to deploy into investments that would make Irish households wealthier.
I'd say the ISK scheme with other guardrails, like annual and total allowance limits, and some offputting (for ordinary folks) tax filing regime is more likely than an ISA type scheme, which is genuinely investor friendly.