Public seating is in place overlooking Hobart's waterfront, and restaurants have started operating in the area pitched as Tasmania's answer to Melbourne's Federation Square.

And late last year, Spirit Super - a merger of MTAA Super and Tasplan - bought the development for $330 million from Trawalla Group, which made it Tasmania's biggest commercial property sale.

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The development is big business, but there's still at least one major unresolved issue: disability access.

On the northern side is Murray Street, where an archway acts as an entrance to the square alongside a hotel. There's also a lengthy set of stairs nearby offering public access. On the southern side is a public entrance from Salamanca Place.

But these non-stair entrances are up a significant incline from Parliament House, the wider Salamanca area and the waterfront.

David Cawthorn, a Tasmanian man who uses a wheelchair for mobility, says this limits access not just for people with a disability, but for anyone who struggles to get uphill.

He wants to see a disability access lift added alongside the stairs on Murray Street, estimating it would cost $400,000 or, as he puts it, "0.1 per cent of what Parliament Square was recently sold for".

His 2016 complaint to Equal Opportunity Tasmania has set off a long-running legal battle that has key constitutional questions, has prompted intervention from every state as well as the Commonwealth itself, and could ultimately have implications for building standards Australia-wide, and the powers of tribunals - whether they be anti-discrimination, residential tenancy, guardianship and more.

Mr Cawthorn's complaint against the developer, Citta, fell at the first hurdle when the company raised a potentially arguable constitutional defence in the Tasmanian Anti-Discrimination Tribunal.

Citta planned to argue that it had complied with Commonwealth standards that say 50 per cent of entrances need to be accessible - and that two out of three in Parliament Square complied. But Mr Cawthorn said Tasmania's anti-discrimination laws would show it would be discriminatory to not provide access to a public place, holding the developer to a higher standard.

It meant a constitutional question - whether Tasmania's laws could override the Commonwealth - had been raised, and the tribunal ruled it therefore did not have jurisdiction to determine it, rejecting the case.

Mr Cawthorn appealed to the Supreme Court, with the full bench ruling in his favour that the tribunal should have heard the case. Justice Stephen Estcourt said the Commonwealth Disability Discrimination Act allowed the "minimum requirements" of discrimination law to operate at state-level, and that people could effectively choose which jurisdiction they wanted to argue in.

Citta appealed this to the High Court, arguing the Supreme Court had incorrectly concluded that the constitutional claim would not succeed. Section 109 of the Constitution also states that when state law is inconsistent with Commonwealth, the Commonwealth prevails.

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When the court granted leave to appeal, every state realised that the ultimate decision could have implications on how its own tribunals interact with constitutional questions. They all intervened.

Tasmania and Western Australia argued the matter had to be heard by a court, not a tribunal.

Other states argued the matter should be split - the complaint should be heard by the Anti-Discrimination Tribunal, but the constitutional question of whether states could impose higher standards than the Commonwealth should be sent to court as a separate matter.

The High Court held a two-day hearing earlier this month during which the question of whether Tasmania's tribunal could have heard the case was the dominant matter.

Acting for Citta, David Batt QC argued that if state-based tribunals were given the ability to decide whether a constitutional defence was arguable or not using any test, it could be "a slippery slope".

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Ron Merkel QC - acting on behalf of Mr Cawthorn - said there would have been no tribunal to hear the complaint, even if Citta's constitutional defence was found to be "invalid".

The High Court might not be obligated to even rule on whether Tasmania's law could provide higher building standards than the Commonwealth, but given the involvement of every state, it could feel obliged to give guidance to avoid going through the process all over again in the future.

Even if the High Court rules that the Anti-Discrimination Tribunal could not hear the case - and so it was ultimately dismissed - Mr Cawthorn could have the ability to start all over again if the court gives guidance on the underlying question.

And during the course of this matter, the Anti-Discrimination Tribunal has been absorbed into the new Tasmanian Civil and Administrative Tribunal. This means should his complaint be raised again, it could be heard by a magistrate who would have jurisdiction to hear it anyway.

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So the High Court's guidance could, finally, allow for the actual substance of the matter to be heard, years after it was first raised, even if it's rejected at this stage. It is expected to rule on the matter in mid-2022.

By that time, Parliament Square will likely be in full swing with leasing opportunities currently available.

And in it's north-east corner sits a concrete landing, next to the staircase and above a portion of building - the possible future location for a disability access lift years in the making.

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