f there isn’t a Redesign this upcoming week and only a spec bump, is it safe to assume the current design will last another couple of years or is apple capable of dropping an all new redesign later this year?
It isn't safe to assume anything. A launch on the 25th is
plausible simply because the iMac is overdue a refresh (and I certainly wouldn't buy a new iMac this week unless it was life or death) - but the current 'predictions' seem to be limited to the sort of reasonable speculation that anybody could come up with (hex core? Knock me down with a feather! With the current Intel range they'd have to "downgrade" to an i3 to get a mere 4 cores in a desktop processor!). Credibility in the bank if you're an "analyst" or a pundit - if you're right you can milk it for all its worth, but nobody's going to remember if you are wrong.
Also the announcement "Show time" sounds like it is going to be mainly about Apple's TV service.
However, if there is a March update it seems unlikely that there would be a re-design for 12-18 months at least - unless it was a
really minor update like bumping the base-model options a bit.
If the rumours about switching to ARM are true (suggested by some, discussed exhaustively in other threads), I doubt that they'd start with the desktops (other than as 'developer specials') but I equally doubt that there would be another major iMac re-design between now and the switch.
Frankly, though 'only a spec bump' to the latest CPUs would be a really big deal because of the hex core thing (and for many applications, a hex i5 would probably be a much better compromise for the iMac thermals than a hot old i7).
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