I wouldn't mind seeing 105 over 4 day tests (you only lose one session - 30 overs), but it will never ever happen for various reasons:
1) Teams already struggle to get through 90 overs in the allotted time as it is.
2) That 5th day is important for the BCCI, who get paid (via advertising) on a daily basis, hence why the explosion of flat tracks in India over the past decade after that Mumbai test in 2004 - to ensure tests go the full 5 days. Cutting tests to 4 days = less revenue for BCCI, which they won't agree to.
3) Geographically, daylight hours aren't long enough in most test venues around the world to get 105 overs in a day.
Only those places that are around at least 40 degrees from the equator - England, NZ and parts of Australia with daylight savings, and earlier sunrises and later sunsets - would have enough adequate, quality daylight to have the playing times according to the specifics of the ECB. If you get any inclement weather, there's absolutely no chance of making that time up at the end of the day due to fading/bad light.
2hr sessions will have to be extended to at least 2 1/2hr sessions (and even then, with all the stoppages that happen in cricket these days like drinks breaks, change in equipment, it will still be pushing it to get 105 overs in). So, the 7-7 1/2 hours in a day of test cricket which currently occurs (3 x 2hr sessions + 40 min lunch break + 20 min tea break + additional 30 mins after scheduled stumps to make up the over rate) will have to be extended to 8 1/2-9 hrs (3 x 2 1/2hr sessions + 40 min lunch break + 20 min tea break + additional 30 mins after scheduled stumps to make up over rate). If 10:30am is the scheduled start of play, stumps as late as 7:30pm is way too late at nearly every Australian venue. Even at the MCG Boxing Day test with sunset in Melbourne at around 8:45pm, since the redevelopment in 2006 with the increased capacity and roof being fully extended around the top grandstand of the stadium, the playing surface is already completely covered in shadow by around 6:30pm. Hobart would probably be the only venue that you could regularly play cricket with a red ball until 7:30pm as not only sunset close to 9pm, but it doesn't have a large roof around the ground, high above the playing surface subtending shadows earlier in play like the MCG or Adelaide Oval.
And then you get to places in the sub-continent like India where scheduled stumps for test matches is at about 4:30pm (4pm in Kolkata, where sunset is earlier).....good luck with trying to start a test match there before 8am. I remember in 2009 when Australia played a bilateral ODI series in India, and the match in Guwahati which started at 8:30am was enough trouble as it was due to the dew on the ground.
In conclusion, Day/night test matches over 5 days are a more realistic proposition of occuring than 105 over 4 day tests
